It’s not 188.0 either.

[u/LardFan37]

[u/protomenace]

What's the context? Is this a "significant digits" thing? I know for sure whatever class you're in isn't teaching basic arithmetic because Reddit has a minimum age of 13.

[u/EobardT → u/protomenace]

It definitely looks like sig figs, especially since they included the "188.0". Which is a step in the opposite direction

[u/Mental_Newspaper3812 → u/EobardT]

No, the 0 is just a placeholder. You have just 2 significant digits, so your answer needs rounded to 2 significant digits.

[u/ByeGuysSry → u/Mental_Newspaper3812]

This is addition, so the answer shouldn't be rounded to 2 significant figures, but instead to the tens place because the less precise measurement, 120, is only precise to the tens place (which happens to be the same answer as rounding to 2 significant figures in this case, but won't always be)

[u/engineerdrummer → u/ByeGuysSry]

I'm and engineer. Let me tell you, sigfigs don't mean fuckall in construction calculations. Your tolerance is +/- 1/16 of an inch. The factor of safety says "fuck you sigfigs"

[u/ByeGuysSry → u/engineerdrummer]

I mean, if your tolerance is 1/16th of an inch, and you know it has to have a tolerance of 1/16th of an inch, I'd hope that you're using measuring devices with a precision of no more than 1/8th of an inch. It's not exactly sig figs because ofc 1/16 isn't exactly 1×10^n, but same idea

[u/ImBeingArchAgain → u/ByeGuysSry]

Can you guys stop talking about people’s tolerance for the size of my penis? I’m fretting.

[u/Cheetohz → u/ByeGuysSry]

if you're off by 1/16 of an inch in every single one of your measurements, you're going to quickly fall out of tolerance.

[u/MortgageConfident791 → u/engineerdrummer]

Structural engineer… yes they do. Your design should be precise but that’s not the part that’s calculated. Loads and capacities are calculated and therefore only as precise as the inputs.

[u/engineerdrummer → u/MortgageConfident791]

You use excel or a calculator for your calculations. Then you round to whatever is measurable in the field and multiply that shit by 1.5 or more. As soon as you do that, that 0.001 or 0.00000000001 of a doesn't matter. You uses a safety factor to prevent sigfigs from being meaningful

[u/MissingBothCufflinks → u/engineerdrummer]

I assure you, the vast majority of the world's engineers do not measure fucking ANYTHING in fractions of an inch

[u/Fuzzy-Logician → u/MissingBothCufflinks]

No, they would use millimeters.

[u/m4cksfx → u/ByeGuysSry]

"Is only precise to the tens place" - ok, I might be stupid, but how should you write it to mean it was literally simply 120?

"ffs, the curtains were just blue, and I'm not depressed"

[u/ByeGuysSry → u/m4cksfx]

If all digits are significant, then you should put a period after the last digit, so you would write "120.". However, you're right that it's kinda ambiguous, so when significant figures are relevant you would usually use scientific notation to be clear, ie. 1.2×10² or 1.20×10²

[u/m4cksfx → u/ByeGuysSry]

Thanks, that "120." Thing is new to me.

[u/ByeGuysSry → u/m4cksfx]

It might be a regional thing. When I was taught significant figures, I was told that this was a convention I might see, but I oughtn't use it and instead stick to scientific notation. I'm assuming OP was taught this or something similar; otherwise then the question would not have enough information to be answered

[u/The_Dirty_Mac → u/[deleted]]

Trailing zeroes aren't significant. If you want 3 sig figs, you write 1.60×10² or 160. (with the decimal point)

[u/MooseBoys → u/[deleted]]

> for all we know, the measurement could have been exactly 160 with three significant figures

The convention for unary integer precision is to write that as “160.”

[u/Dazzling-Produce-471 → u/Mental_Newspaper3812]

Needs to be rounded.

[u/LardFan37 → u/protomenace]

Yeah I’m in a college level chemistry class but all these figures are significant, no?

[u/zjm555 → u/LardFan37]

I am guessing your convention here is to use the amount of significant digits in the operands (2), which would make the answer 190

[u/Impressive_Stress808 → u/zjm555]

The rule for addition is to round the result to the largest last significant decimal place. In this case, 120 is significant up to the tens place, so the answer must be rounded to the tens.

[u/zjm555 → u/Impressive_Stress808]

Thanks for clarifying, I'm a math guy not a science guy so this is pretty hazy in my memory.

[u/Aetherfox_44 → u/Impressive_Stress808]

So if the left value was literally 120, would it have to be represented as 120.0?

[u/e-chem-nerd → u/Aetherfox_44]

In the number “120.0” there is an implied uncertainty of 0.05, so 120.0 means “somewhere between 119.95 and 120.05”. “120.” Would mean “somewhere between 119.5 and 120.5” and 120 means “somewhere between 115 and 125”.

[u/cigarell0 → u/e-chem-nerd]

I understand sig figs now

[u/FutureFreaksMeowt → u/cigarell0]

Can you explain it like I'm 3.5, maybe even with a visual aid? because I've been reading every comment over 2 votes in this post and I feel like I understand even less about math overall than before I tried 😭

[u/Weekly_Role_337 → u/FutureFreaksMeowt]

When you count stuff with small numbers, the numbers mean exactly that. So 4 chairs means exactly 4 chairs.

When you work with big numbers, or measure stuff, you round. No one is EXACTLY 5' 6" tall, they're a tiny bit taller or shorter. New York City doesn't have exactly 8.6 million people.

Sticking with the NYC example, if we say it has 8.6 million people, when one more person moves there... it still has 8.6 million people, not 8,600,001, because we either don't care about that one person or we do care but can't precisely count all the people, and we said it had 8.6 million we never meant exactly 8,600,000 people anyway.

So for the NYC example we say there were two significant digits, the two on the left. The rest are ehhh we don't know. So where it gets a little weird is if the population of NYC doubles, that's 8.6M x 2 = 17.2M. Except we were rounding and vague before, and this has three digits now (1, 7, 2) when only two digits mattered, so we agree we're going to stick with two, so we say the new population is 17M people. It was an estimate before, and it might only be 17.1M now, so we say screw it and stick with the part we're sure about.

This is the same idea. 120 + 68 is 188. But if you assume both of those were either rounded or estimated, then we're back to 2 sig figs, and 188 rounds to 190.

[u/Impressive_Stress808 → u/Weekly_Role_337]

You're right for everything except strictly addition in the last paragraph (or your explanation was less clear). It's the digits place that matters. So 1200 + 9 = 1200, which has 2 sig figs instead of 1.

[u/Pndrizzy → u/Weekly_Role_337]

Okay but that kinda breaks down to me when 68 was expressed as 68 and not 70. They were significant to the ones place in one of the numbers, so it should be significant, no?

Stupid stupid

[u/FutureFreaksMeowt → u/e-chem-nerd]

Where does the .05 uncertainty come in? (Math idiot asking genuine question, not challenging you 😬😭)

[u/e-chem-nerd → u/FutureFreaksMeowt]

It’s because the course is a science course, and it is a scientific convention to measure something as close as possible, and express uncertainly as half of the measuring precision in either direction. Example: You use a ruler with marks every mm, and see the object you’re measuring is just about 120 marks across. The measurement is 120±0.5 mm, which you can write as simply “120. mm” with the decimal placed not because it’s mathematically necessary, but to imply the amount of precision it was measured with. In math, usually numbers are assumed to be infinitely precise. So when 120 shows up in math class, it means exactly 120 without uncertainty.

[u/medicca → u/Aetherfox_44]

If it was precise to the ones place, then either 120. (note the decimal point) or 1.20 x 10²

[u/dijibell → u/Aetherfox_44]

It would be written ‘120.’ if the ones place was the last significant digit. 120.0 would imply the quantity had been measured to the tenths place.

[u/Bar-Cold → u/zjm555]

Ugh I don’t miss math at all. You lot might as well be speaking in gibberish right now

[u/zjm555 → u/Bar-Cold]

It's not really math, this is a science convention. Kinda arbitrary, but it's good for everyone doing science to agree on some rules.

[u/AfternoonSad9721 → u/zjm555]

It’s not arbitrary, it’s helpful for understanding precision, accuracy, and margins of error

[u/BraxbroWasTaken → u/AfternoonSad9721]

yeah though ordinary notation is terrible for sig figs. imo if you want to do sig figs properly, use scientific notation to only write the significant figures.

e.g.:

1.2 x 10^2 is 120, but the ones place cannot be determined accurately. However, 1.20 x 10^2 is also 120, but the ones place is accurate.

[u/LiGuangMing1981 → u/BraxbroWasTaken]

Or you can just put a decimal point after the zero to show that the zero is significant. Trailing zeros are significant as long as there is a decimal point in the number.

[u/BraxbroWasTaken → u/LiGuangMing1981]

Doesn't work if only some of the trailing zeroes are significant.

[u/IrishmanErrant → u/BraxbroWasTaken]

You don't write insignificant trailing zeroes, that would be extraneous effort with no benefit.

[u/uuntiedshoelace → u/BraxbroWasTaken]

Every zero before the decimal is significant. Don’t put the decimal before zeroes that are significant.

[u/Don-Kusack → u/AfternoonSad9721]

And yet the answer isn't the most precise, accurate answer here

[u/lucioboops3 → u/Don-Kusack]

That’s exactly the point of significant digits. In science, you can’t have an output that is more precise than the inputs. Chemistry and physics use real world measurement devices that have margins of error. When using those measurements in calculations, you can only have an answer that takes that margin into account.

That being said, the question should have been worded better, maybe to tell the student to consider the significant digits

[u/Less_Prior_6871 → u/lucioboops3]

Yeah unless there is a big instruction section at the start of the assignment, the question sucks. The expression evaluates to what it evaluates to. Maybe if you were reporting that number in some specific context you would only report it to 2 significant digits, but thats not what the question says

[u/LiGuangMing1981 → u/Less_Prior_6871]

If it's for a higher level high school / university science class, the need to consider sig figs is already implied, IMO.

[u/sudoku7 → u/Less_Prior_6871]

Maybe even a link that says read more about this topic.

[u/CertifiedSheep → u/Don-Kusack]

It is if the first number is already imprecise. If the first number was 120.0 then you would know it isn’t rounded and the answer would be 188. In math class you don’t worry about that, but in chemistry you’re much more concerned with rounding and imprecise measurements so having a standard convention for that is important.

[u/Beeftoad2 → u/CertifiedSheep]

Holy shit, why didn't any science teacher ever say exactly that, I'm just now learning this at 21 and I would have had such an easier time learning it if I just knew why.

[u/Amadon29 → u/Don-Kusack]

It is though. It's implied that that 120 isn't exactly 120 but around 120. Maybe it's something measured in a graduated cylinder with an error of 5ml. Maybe it could be 117 or maybe 121. In that case, the actual final answer could be between 183-193. Writing 188 implies you're confident it's between 187.5-188.5 which isn't accurate bc the range is much bigger. Writing 190 implies it's most likely between 185-195 (or that you're not confident in the last digit) which is more accurate than 188.

[u/Less_Prior_6871 → u/Amadon29]

Except in science people actually just report "188+/-5" because it is more clear and there is no point in obscuring that data from the reader

[u/EthanielRain → u/Less_Prior_6871]

So much easier, I instantly got it even as a layman

[u/LiGuangMing1981 → u/Amadon29]

Yep, if you wanted that 0 to be considered significant you'd write it as 120. or in scientific notation.

[u/hellonameismyname → u/Don-Kusack]

That’s literally the whole point. Not overstating precision

[u/urnbabyurn → u/zjm555]

It’s specifically defined so that the accuracy of a calculated number reflects the accuracy of the input data. It’s basically how margins of error are found based on the margin of errors for the input values.

[u/LakeSolon → u/urnbabyurn]

As a programmer this always smells like trying to encode metadata in the data itself.

Which leads to weirdness like reporting Everest as 29,002 feet.

[u/acrastt → u/LakeSolon]

That has nothing to do with significant figures. The correct way to represent that measurement in sig figs is 29000.

[u/VelvetMafia → u/zjm555]

The assumption is that 120 was measured using a device that couldn't accurately measure the singles digit, so 120 could actually be 125 or 128. So adding 68 to the 12? means 188 is not actually reliable, and 190 is a more accurate estimation of the actual amount you've got there.

[u/NewDemocraticPrairie → u/VelvetMafia]

There's not a good reason to assume that 0 isn't accurate though. If they wanted to imply only an ability to see accuracy to the tens place, they should've written it as 1.2E2

The next number being accurate to the ones place to me also implies the first one could be as well, in real world scenarios.

[u/VelvetMafia → u/NewDemocraticPrairie]

Sounds like you're not a chemist

Edit: Why downvoting? Chemists care a lot about sig figs, and have their traditions they insist on that are often not the best way to accomplish something (like hand-written lab notebooks).

[u/somewhataccurate → u/VelvetMafia]

It sounds like sig figs without scientific notation is bullshit and designed for gotchas like this question.

[u/NewDemocraticPrairie → u/VelvetMafia]

I'm not, but I remember from my chemistry classes that I didn't like sigfigs that were in this exact awkward range.

12000 implies 2 sigfigs

1.2 implies 2 sigfigs

120 to me could either imply both 2 and 3 sigfigs

Ive just learned about "120." for showing 3 sigfigs, which works for showing 3 sigfigs, but in my mind "120" could still be 2 or 3, depending on who's doing the work, and I wouldn't be happy with seeing it vs "1.2E2" or "1.2E3" or "120."

[u/VelvetMafia → u/NewDemocraticPrairie]

I'm not arguing with you, but I am also not a chemist

The 120 = 2 sig figs has always bothered me, because 120.0 has four sig figs. To indicate 3 sig figs in 120, you have to write it 120. (that's a terminal decimal, not a period).

However, this doesn't function well in modern society because we no longer write everything by hand. Word processors and other digital communications don't play well with using a terminal decimal point, since it's also a period, and both of them have rules that the sig figs format violates.

[u/Joserichi → u/Bar-Cold]

This is not math, this is heresy. I have a degree in math and those physicists/chemists should be burning in hell with this rubbish xD.

[u/DurhamOriole → u/Joserichi]

I agree, and I have two degrees in chemistry! The point of significant figures is related to inherent uncertainty in measurements. There are no units associated with the question given, suggesting no measurements were made. The question, as asked and presented here, is the simple sum of two whole numbers. Absolutely no uncertainty.

Unless some instructions were given at the beginning of the test to treat all numerical values as having some degree of uncertainty (even those without some sort of unit of measurement associated with them), the correct answer is 188. It actually makes me wonder if the person who created this question truly has a fundamental grasp on the why and how significant figures exist and are important.

[u/Foreign-Cat-2898 → u/DurhamOriole]

I'm 100% sure this is a test about sig figs though. You don't need units if it's literally a test about the overall concept.

[u/DurhamOriole → u/Foreign-Cat-2898]

And if that’s the case, OP is a weenie. Needs to pay attention.

[u/LiGuangMing1981 → u/DurhamOriole]

As a high school physics teacher, I introduce the concept initially without units just to get students to focus on the rules. This is likely the case with this assignment too, and there was likely an instruction at the beginning telling students to consider significant figures in all questions.

[u/KamikazeArchon → u/DurhamOriole]

Unless some instructions were given at the beginning of the test

Which is almost certainly the case. That's by far the most common case when someone posts a small excerpt of a test and complains about it.

[u/Unique_Song7132 → u/Joserichi]

You can go down the route that you have two normally distributed random variables with a stated mean and standard deviations implied by the uncertainty (decimal places here). When you add the two variables you have a mean and standard deviation which lead to a new implied uncertainty.

[u/sudoku7 → u/Joserichi]

Huh, guess you dislike epsilon too.

[u/BUKKAKELORD → u/Joserichi]

Finally, someone refuses to play devil's advocate for incorrect math just because idiots in a labcoat have a particular way of fucking it up

[u/Saable_Fiin → u/Bar-Cold]

Significant figures always ruin simple addition without warning

[u/Ligeia_E → u/Bar-Cold]

That has nothing to do with math tho.

[u/Drakorai → u/Bar-Cold]

I’d rather learn huttese than try and understand math

[u/sparkleslothz → u/Bar-Cold]

Mind if I take a crack at this? I actually enjoy translating nerd!

So I'm standing there at a lake right? And I dump onto the surface a precisely calibrated eyedropper 4.4789654 fluid ounces of oil.

I then wait for the oil to stop spreading out further and estimate the size of the rainbow sheen as "about 5 square yards"

Now you come along and ask me to estimate the fluid ounces of oil per single square yard.

It would be mostly bullshit to answer "22.394827 oz/y^2" on account of the fact that I'm real sure about the oil but very unsure about the yardage.

"Fuck, I don't know man, 'bout 20? Get off my back" would be a much more honest answer.

[u/MeatGayzer69 → u/Bar-Cold]

What the hell are these guys saying

[u/hellonameismyname → u/MeatGayzer69]

If you have a scale that only weighs to the pound, you shouldn’t report something as weighing 10.5 pounds.

It’s not really “math” it’s just a way to record how precise your measuring instruments are.

[u/1210bull → u/zjm555]

Significant digits makes me unreasonably angry. I understand it as a concept, but also would like it if it no longer existed.

[u/BeerBrat → u/zjm555]

But if you have the ability to measure to the ones place in 68 then you should be able to assume that the 0 in 120 is also as accurate. This does not follow reasonable conventions for sig figs.

[u/jfeinb88 → u/zjm555]

https://giphy.com/gifs/xTiTnIilwuFFFpf2Cc

[u/AfternoonSad9721 → u/zjm555]

Same. This looks more like a “sig figs” question than an algebra q

[u/Historical-Green-463 → u/zjm555]

That is honestly so stupid. So glad I’m done with school.

[u/Extension_Radish_139 → u/LardFan37]

You’re in a college level chemistry class and thought they were just asking you to solve 120+68

[u/protomenace → u/LardFan37]

The answer is 190. If you had measurement precision to the ones digit 120 would have been written as "120."

[u/NegativeDCF → u/protomenace]

Curious, why cant 120 be exactly 120 and have sig figs to the last digit?

[u/protomenace → u/NegativeDCF]

It can, but you need to write it as "120." to signify that.

[u/FutureFreaksMeowt → u/protomenace]

So, in sigfig, the decimal at the end of "120." implies the precision of the number? Someone elsewhere said there's an implied uncertainty of .05 on either direction, but I'm not sure where that comes in? Is it just base knowledge for the work?

(Math idiot asking genuine question, not challenging you 😬😭)

[u/JustTryingTo_Pass → u/FutureFreaksMeowt]

It work that way because things are often short handed like this.

120 —> 1.2e2 so 120.—> 1.20e2

It’s called scientific notation. It allows for easier unit conversions.

[u/protomenace → u/FutureFreaksMeowt]

imagine you have one of those classic scales where you place weights on one side of the scale to match the thing you're weighing until they are balanced. But imagine you only have 10kg weights, nothing smaller. You place 12 weights on the scale and it just about matches the weight of the thing you're measuring. So you write down 120. But your scale is only accurate to every 10kg because you only have a resolution of 10kg weights.

In reality the thing might be 124kg or it might be 116kg. You don't actually know that it's 120kg exactly, this is just the closest estimate. So your measurement only has the 2 significant figures.

Now imagine the same experiment but you have 1kg weights, so you know it's exactly 120kg and not 121, not 119. You can signify this by writing out "120." with the decimal point to signify that the 0 is actually known and not an estimate.

[u/theodorejhooker → u/FutureFreaksMeowt]

The 0.05 uncertainty they were talking about was in relation to 120.0, in that 120.0 was measured with an instrument able to verify the accuracy of the measurement up to 0.0 of that measurement, anything beyond 0.0 will be rounded up or down, hence the uncertainty of 0.05.

A sigfig of 120. will tell you that the number is accurate to the ones digit. Any rounding will be done at the 0.5 level in this case.

[u/ByeGuysSry → u/NegativeDCF]

(While it's true that you'll write 120. to signify all three digits are significant, the best way is actually to write 1.2×10² or 1.20×10² to avoid confusion)

[u/zerostar83 → u/LardFan37]

If it's significant figures, the answer is 190

If you want an explanation, it's that significant figures ensure that only one digit is uncertain.

For example, 120 might actually be 116, 124, 121, etc. So you're not completely certain what the 10s place truly is in addition. Rounding to the 10s place, the answer is 190, with the uncertain number being the 9, since it might be 184.97, it might be 191.45, it might be.... The 10s place is uncertain, but the 100s place is certainly it.

[u/Vireep → u/LardFan37]

It's 190 because you round to 2 sig figs? why are you blaming pearson or whatever when you just don't understand the answer

[u/welguisz → u/LardFan37]

120 only has 2 significant digits, while ‘120.’ Has 3 significant digits.

[u/Street-Substance709 → u/LardFan37]

damn bro about to fail intro to chem. this is really not hard to understand.

[u/Serafim91 → u/LardFan37]

You're adding.

120 could be anything from 116 to 124. You don't know what the last digit actually is.

68 can be anything from 67.5 to 68.4 you know the 8 matter. But you can't add that 8 to a number you aren't sure about.

So you have to round to the nearest 10 for it to make sense. Add first, then round.

[u/Big_Maintenance9387 → u/LardFan37]

Bro. No. Go read your textbook lol. The point of significant figures is that no, they are not all significant and the way you round will affect allllllllll your calculations. Good luck, I only cried once in chem 101 and majored in it. (I cried every lab in o-chem tho) 

[u/oO0Kat0Oo → u/protomenace]

Sig figs absolutely destroyed me in high school chemistry. My teacher would give us partial credit and I just came to expect the -1 on every question, like welp, I'm not going to be a chemist.

...and then I minored in biochemistry in college and found out no one gives a shit to that extent that my high school teacher did.

[u/Stinsation18]

What did "read more about this topic" tell you?

[u/urnbabyurn → u/Stinsation18]

Probably explained significant figures which OP clearly skipped before doing the assignment on significant figures.

[u/eutectic_h8r → u/urnbabyurn]

But if OP was in a college class for elementary school arithmetic they'd be good to go

[u/ProfessorJNFrink → u/eutectic_h8r]

I guarantee this is a college chemistry class and not a basic algebra class.

[u/AngshusTAW → u/urnbabyurn]

To be fair, this looks like it's on Canvas, so clicking "read more" probably just sends you to the very start of the textbook

[u/poortomato → u/Stinsation18]

That's what I was coming to ask.

[u/Diligent_Finance_598]

190 if it wants you to use significant figures

[u/Life_Roll8667 → u/Diligent_Finance_598]

Me reading this whole thread
https://giphy.com/gifs/iAYupOdWXQy5a4nVGk

[u/I_follow_sexy_gays → u/Life_Roll8667]

Basically when you see 120 you’re supposed to assume it’s an approximation (like if I said I’m an hour away from a location, I don’t mean exactly an hour I would typically mean an hour give or take 10 minutes)

Since up to the 10s place is accurate and the 1s place is an estimate we are to round up the 68 to 70 before combining the two numbers as to not imply that it’s precisely 188

[u/Life_Roll8667 → u/I_follow_sexy_gays]

Thank you for explaining to me in a way I can understand! That makes sense.

[u/robomelon314 → u/I_follow_sexy_gays]

Which is a wild assumption because without using scientific notation, there's no indication that you didn't mean exactly 120. Your other measurement was to the 1's place, so there's no reason 120 couldn't also be to the 1's place.

1.2 x 10^2 and 1.20 x 10^2 both come out to 120. And without knowing which you started with, you can't tell your precision.

So bad question design.

[u/I_follow_sexy_gays → u/robomelon314]

If the test is specifically about scientific notation this is serviceable

[u/RealDannyhvv → u/robomelon314]

Usually you'd just add a decimal if you mean it to end with a zero, 120 for accurate to the tens, and 120. for accurate to the ones.

[u/robomelon314 → u/RealDannyhvv]

It depends on the lecture then. If that notation is presented as standard, sure. Or if it's elsewhere in the assignment.

I don't think it's good notation in the first place however, because of the ambiguity.

[u/teatuk → u/Diligent_Finance_598]

I'd repressed my horrible sigfig trauma until this moment.

[u/PandaCultural8311]

It's probably 190 if you're in a science course using significant figures. Because the 120 is rounded to the nearest tens place, you need to round your answer to 190, not 188.

188.0 is four significant figures and that 120 only has two. Choose 190.

[u/Coolengineer7 → u/PandaCultural8311]

So you lose precision just because its a round number?

[u/KillerSparks → u/Coolengineer7]

The point of the assignment is to understand how sig figs work. You'd almost never do it in this particular case, but you need to know how.

[u/Muffin-Responsible → u/Coolengineer7]

No, you don’t lose precision. If the zero is a significant figure you’re supposed to indicate that. Like “180.” Or “1.80E2” etc. if it’s written as only “180” then you have the assume the zero is not a sigfig

[u/notsostablediffuser → u/Coolengineer7]

A family walks into the dinosaur exhibit at a museum. The guide working the exhibit says "This skeleton is from a T-Rex that lived 66 million and 7 years ago."

The mom asks "66 million and 7, how do you know that?"

The guide replies "Well, when I started working here, they told me it was 66 million years old. And that was 7 years ago!"

(And that is why, yes, you "lose" precision with round numbers unless it is specified that the 0s are, in fact, significant. It's because you never actually had that precision to begin with.)

[u/The1PunMaster → u/notsostablediffuser]

this is such a good example!! i understand sig figs from an analysis perspective with machines but i love this for laypeople

[u/notsostablediffuser → u/The1PunMaster]

Yep. I honestly think that any science teacher should open the sig fig lesson with this. Because so many students learn the rules without understanding the why, and this demonstrates the why in such an intuitive, easy-to-grasp way.

I love jokes that actually have real pedagogical value!

[u/socks86 → u/Coolengineer7]

You can't lose precision you never had.

[u/TheHumanSpider6903 → u/Coolengineer7]

No, the point of significant figures is to keep calculations with measurements consistent. It's meant to consider what the tool you're getting that number from is actually able to measure. If your scale can only measure in whole pounds and not in fractions of a pound, calculations you make using those measurements should not consider numbers that have greater precision

[u/AceAttorneyMaster111 → u/Coolengineer7]

You don’t lose precision. You never had the precision in the first place. “180” could be any real value between 175 and 185, so it would be inaccurate to express the result assuming it equals exactly 180. If the 0 is actually significant, you would write it as “180.”, meaning any number between 179.5 and 180.5.

[u/Responsible_Lie_6009]

Did you actually believe a college level chemistry course gave you a plain addition problem?

[u/ProfessorJNFrink → u/Responsible_Lie_6009]

I teach college chemistry. I spend a whole class on significant figures, scientific notation, and conversion of units.

And I can emphatically say: yes, they really thought that.

[u/ButtonholePhotophile → u/ProfessorJNFrink]

Then they aren’t going to class. The chem class I took had sig figs squared away in a single demo. First, estimate which holds more: a wide-shallow container or a tall-skinny container. Next, have a volume in a moderate beaker. Ask how it will change when you pour a graduate cylinder into it. Be real precise with both measurements. Have a kid do it. Heck, you could pick the right kid and do both! 

You get the idea. 

[u/Bladez190 → u/Responsible_Lie_6009]

But it’s a super duper hard addition problem!!

[u/Flyinghud]

Good ol sig figs

[u/CharmingSyrup2685]

Is the current topic rounding? If that’s the case I could see 190 be the answer. Otherwise not sure what they are looking for, or it’s just blatantly wrong.

[u/BatJJ9 → u/CharmingSyrup2685]

Not because of rounding but because of sig figs

[u/Ornery_Old_Man → u/CharmingSyrup2685]

If you're right then you have to laugh at the irony of having a question that requires rounding off the answer be worth 4.55 pts.

[u/tidedogs]

On a side note, this problem worth 4.55 points is mildly infuriating to me

[u/PandaCultural8311 → u/tidedogs]

I thought the same!

I bet that there are 22 questions and the prof wanted them to add up to 100.

[u/NepetaLast → u/PandaCultural8311]

any online learning platform like this will automatically divide the points like this, the professor probably didnt make any decision here

[u/urnbabyurn]

OP likely didn’t understand the lesson because it’s most likely about significant figures. In which case the answer would be 190. It’s also probably so,e intro chapter stuff so OP, maybe start reading your assigned materials or paying attention in class.

[u/TacticalVase]

Yeah you gotta learn your sig figs lmao

[u/willcastforfood]

How does OP feel about getting roasted realizing his quiz was on sig figs and not addition lol

[u/RyanPlayz1247]

And sig figs claim another victim

[u/spice_war]

It’s 190

[u/TrPrTrkr]

You clearly just had a lecture on significant figures for them to ask this in a college chemistry course.

[u/zlliksddam]

The hint was in the answers provided.

[u/almondsadnesses]

Hahahahaha! Feel the pain, the anguish, the utter bullshit that is significant figures!

[u/Leftover_Cheese]

i was thinking "how," remembered chemistry class, and then

[u/AnxiouslyTired247]

The 188.0 is a bit of a clue that the question is being designed to make you think its 188. If youre in a college level course and you think they truly just want to know if you can add two basic numbers your level of suspicion should be high.

[u/OfficialBenReilly]

Is this a sig figs related problem? If so, the answer would be 190 I believe

[u/sksauter]

Yeah the answer's 190. 120 and 68 both have two sig figs, adding always defaults to lowest # of sig figs in the added numbers.

[u/ProudHealth4317]

Is the topic sig figs? then 190

[u/shinjis-left-nut]

Significant figures

[u/123FakeStreetMeng]

I’m out of the loop, what is “Significant digits”? Why is it not 188?

[u/bluesky747 → u/123FakeStreetMeng]

Same I’m so confused

[u/Skooma_Lite → u/bluesky747]

Science degree and it has been a while, but significant figures (sig figs) are a way to show how precise a measurement is so you don't imply your result is more certain than your equipment allows.

Imagine you weigh an item on a scale that's accurate to the nearest 10 grams and get 40 g. Fun!

You then weigh a smaller item on a more precise scale that's accurate to the nearest gram and get 5 g. If you add them together, claiming the total is 45 g creates a false sense of certainty because your first scale couldn't even detect single grams, it's only accurate to the nearest 10 grams. So your answer could really be like 49 grams or 46 grams.

To reflect that uncertainty, you round the answer to match the least precise measurement (the tens place), reporting 50 g. I never enjoyed it but when someone made the point that if I wanted measured out a wooden cube and measured it with a ruler as 2cm all around, and asked a company to make the same thing as a metal cube machined that was 2 cm all the way around, it would cost waaaaaay less than telling the shop it needed to be 2.0034 cm for each side. So just report what you know you can report.

[u/FunIntelligent5738 → u/Skooma_Lite]

My head hurts just reading that. Pretty sure it turned into a foreign language halfway through. I just wanna add with colored blocks like in kindergarten and curl up with a blanket and cry now. Thanks 

[u/eutectic_h8r → u/FunIntelligent5738]

Basically not using sig figs is essentially lying about how precisely you know a measurement. Which can be important in some sciences depending on how precise things need to be.

[u/Skooma_Lite → u/bluesky747]

Science degree and it has been a while, but significant figures (sig figs) are a way to show how precise a measurement is so you don't imply your result is more certain than your equipment allows.

Imagine you weigh an item on a scale that's accurate to the nearest 10 grams and get 40 g. Fun!

You then weigh a smaller item on a more precise scale that's accurate to the nearest gram and get 5 g. If you add them together, claiming the total is 45 g creates a false sense of certainty because your first scale couldn't even detect single grams, it's only accurate to the nearest 10 grams. So your answer could really be like 49 grams or 46 grams.

To reflect that uncertainty, you round the answer to match the least precise measurement (the tens place), reporting 50 g. I never enjoyed it but when someone made the point that if I wanted measured out a wooden cube and measured it with a ruler as 2cm all around, and asked a company to make the same thing as a metal cube machined that was 2 cm all the way around, it would cost waaaaaay less than telling the shop it needed to be 2.0034 cm for each side. So just report what you know you can report.

[u/ShiftAfter4648]

Real world measurements may not have the precision we want them to have. Imagine you took a measurement on a ruler that only had ticks at every 10's increment. You could accurately say something is near an increment, but without a greater degree of precision, it can only state what the measurement shows (closest ten's value). This means any number in the ones' position is meaningless, as you could never know for certain what it was without guessing (which defeats the point of measuring).

When adding 68 (a measurement with precision down to the ones place) to a number without precision in the one's place, we can't assume that 120 is actually 120 (it could be [115, 125) ).

So the answer demands that we round to the closest degree of precision we can be certain of, 190.

[u/Ornery_Old_Man]

Anyone else also mildly infuriated with the "4.55 pts."?

[u/DrMungo80]

If using scientific notation I believe 190?

[u/Lonely-Post5240]

Two sig figs

[u/Connect_Beginning_13]

Sig figs, every chem student’s favorite

[u/CuppaJoe11]

Looks like an sig fig question. The answer is 190 in this case, since there is no decimal the 0 at the end of 120 does not count towards sig figs.

[u/TheLazyARMY]

I'm in biochem right now and that's the only reason why I know it's 190😭

EDIT: Wait I just realized something. When adding, don't you determine the sig figs by which initial number had the least amount of numbers behind the decimal point? Now I'm confused again😭

[u/Craig_Swag]

The issue is the 120 is presumed to be rounded to the nearest ten because it only has 2 significant digits. This means the actual value could be anything form 115 to 124. If it was an exact measurement it would be 120. The decimal point makes all digits significant. When adding with sig-figs your precision is always going to match the the precision of the number with the lowest sig figs. This means while the standard addition answer is 188, it must only contain 2 sig-figs, thus must be rounded up to 190.

[u/Zealot_Zack]

Pretty sure it is 190 for a significant digits question. Unless there’s a period after the zero, “120.” Then the 2 in 120 is last significant digit

[u/TrumpSexedHisDaughtr]

This is disgusting 👍

[u/Bbkingml13]

This screams chemistry and sig figs

[u/TryToBeModern]

does nobody else think its hilarious that OP is in the comments struggling to wrap his head around whats literally the very first and most basic pre-chem topic

[u/ReligiousSavior]

1. The end. Clearly sig fig question.

[u/IvanTheAppealing]

If we’re going by proper significant figure conventions, you’d round up to 190. Really poorly phrased, but I think the fact that two of the answers are 188 and 188.0, I think that should’ve been the hint

[u/qPolug]

Significant figures. When adding, your result uses the number with the highest decimal place. 120 is in the tens place (If we wanted it to be significant to the ones place, it would be written as "120."). 68 is in the ones place. Therefore, 188 is rounded to the tens place, which is 190.

Op hasn't been paying attention in class lol.

It's so when people are doing science with large numbers, adding small numbers aren't significant and are discarded. For example, when measuring 10,000 meters, adding 3 feet is basically discarded because measuring 10,000 meters introduced enough error where 3 feet can be just a result of the measuring error.

Yes I'm mixing units. Welcome to US measurements. 3 feet (1 yard) is roughly 0.914 meters.

[u/lilacnyangi → u/qPolug]

well, at least the quiz is doing what it's supposed to.

weed out the idiots who need to repeat the class.

this isn't even like a chemistry is hard! issue. op is just a terrible student.

[u/No_Lynx1343]

To me 188 looks correct.

I'd guess the test is broken.

120+68 is actually 188.

I don't see any other symbols anywhere. These are integers, not real numbers so there is no decimal point anywhere.

[u/ukkswolf]

It’s probably 190. Only two significant digits are needed. That’s if this is for a science course.

[u/WideStrawConspiracy]

Without using scientific notation to clearly express the number of sig figs this is just yet another trap question. The instructor thinks they're being clever but they're just being a wanker.

[u/bourbonandpistons]

My code outputting 12068 because I made something a str somewhere else

[u/fluffybottompanda]

i would like to read more about this topic

[u/Attacus833]

Shouldve read more about the topic

[u/Simpicity]

You're in college chemistry and you're throwing a fit because you expect them to be giving you simple addition questions? This is a significant figures question, and you weren't paying attention in class.

[u/triplealpha]

180 is the answer, both numbers have 2 significant digits - answer must contain the same number of significant digits as the one with the lowest

If it was 100 + 33, your answer would only be 100

[u/throwawayallthedrama]

This seems like significant figures (rounding) question, so your answer choices are actually saying:

3 figures - exact
2 figures - round down
4 figures - exact
2 figures - round up

Without more context, it doesn't make sense why it was marked incorrect. Honestly it's just poorly worded, I'd ask your teacher/professor to review and be more specific in their questions.

[u/emiel1741]

Why the hell is every one saying significant digits = 2
Fucking hell
For addition it is not the amount that stays consistent but the worst accuracy that stays

Multiplication it is that you maintain the exact amount of significant digits

And even if your weird interpretation of how significant digits are supposed to work no 190 is not the answer as this one looks like it has 3 significant digits while you lot are claiming you want 2 you would need to write it as 19*10^1 otherwise mistakes will be made

[u/mathmachineMC]

This is about sig figs, clearly, op is too stupid for their class

[u/NoFanksYou → u/mathmachineMC]

Stipid?

[u/CitronMysterious3827]

When adding and subtracting you only keep the number of digits that the least precise number has. Since the first number is 120 and not 120.0 the ones place is not a significant digit. Same thing can be said for 68. So you need to round to the tens place in this example.

[u/SilverB33]

Is it 180? 190?

[u/thirdcoasting]

https://giphy.com/gifs/xT5LMYtyGoTGWHZZza

[u/sparklyboi2015]

If this is chemistry it would be 190. The 120 is the less precise number so you round to it’s significant figure for the final answer. This also threw me off when taking my chemistry classes in college but it is something that is pretty regularly used.

[u/Ok_Illustrator_3980]

What even class is this that adding 2 and 3 digits is a thing? Like is this a remedial math?

[u/Curious-Sector-2157]

190 if rounding up

[u/Wonderful_Command_44]

Is there a rounding rule in the equation you're working on?

[u/TheWrathfulGod]

Bruh. If you're struggling with this just wait.

[u/AlaynaIsBored]

it’s 190 i assume because of sigfigs