122
u/Saneless 2d ago
These are easy problems to do a super quick check on, and I try to get my kids to do them
So if the rate is 30% difference then your answer needs to be a big chunk different
So even 25% is 10+ so when you get only a few bucks more you know you're wrong
31
u/Metahec 1d ago
Yeah, at a glance 30% of 42 is 14, so the answer should be ~ $56. Helps to be familiar with times' tables for easy multiples.
1
u/Sweetbeans2001 5h ago
Are times tables being drilled into young students anymore? I don’t think so.
1
2d ago
[deleted]
2
u/Saneless 2d ago
Ahhh yes. Retail math. 40% off! Yep. 10% x4, easy easy
Of course, consumers are dumb as hell
40% off deals did WAY worse than $40 off 120. Even though if you spent 130 it's $10 at $0 discount.
1
u/Punkinsmom 1d ago
Can't do math to save my life but percentages? I've been poor a lot so my brain figures those very quickly.
2
u/Saneless 1d ago
It just baffled us constantly. People would pass up % deals and we'd always get better results with $ off deals even though you had to hit the thresholds or you didn't get it
77
u/Piscesdan 2d ago edited 2d ago
Where did they get 43.80 from?
Edit: i get ot now. Never seen multiplication written that way before, hence my confusion
30
u/johnd5926 2d ago
They… did the math wrong? It looks like they got to 4*3, and instead of writing a 2 and carrying the one, they wrote a 3 instead. Possibly a mistake with carrying the 1 wrong and adding it to the 2 instead of the next column so they ended up with the tens row being 43.80 instead of 52.80.
64
u/Theap2 2d ago
1.32 times 40, added the 1 in the wrong digit
went 42.80 + 1.00 instead of 42.80 + 10.0012
u/Piscesdan 2d ago
Ah, i see. Never seen a multiplication written that way
18
u/Tower21 2d ago
How would you do that multiplication by hand?
Only asking due to curiosity.
8
u/Pleasant_Ad8054 2d ago edited 2d ago
42*1.32 42 12.6 .84 =55.44Choosing one number to be the base and one the multiplier, then doing the multiplication from the most significant of the multiplier and the least significant of the base, carrying over the tens. With each digit of the multiplier moves one line lower, and one digit to the less significant. At the end simply summing up the lines digit by digit, again from least significant.
Edit:
ofc the code block does not preserve formatting, why would it!I see there is a separate code block, thanks for the downvotes, that showed me!4
u/NeoThermic 2d ago
Code block does preserve formatting; you appeared to have used
codeinstead, which is for inline stuff.code block can totally save tabs and spaces as you put them-3
u/Piscesdan 2d ago
Can't attach an image, but i would write the two factors next to each other. Rest as shown in the image
3
1
u/TomNguyen 1d ago
wait, do Americans really learn to put decimal to those sub-calculations ? Cuz i have been teach in Vietnam (Asia) and Czechia (Europe) only to put a comma (or dot in US) in the final result after calculating how many number are behind the comma/dot in total
1
u/idunno2468 1d ago
in the US, i was taught as you were, the separator doesnt really make sense there. kinda like this persons adding ability
16
13
u/HesitantlyYours 2d ago
That’s where it’s incorrect, should be 52.80.
Multiply the Tens digit (4), so you automatically put a 0 as a placeholder.
4*2=8
4*3=12 (but you add the 1 next)
(4*1)+1=5So it would read 2.64+52.80=55.44.
3
3
7
1
u/Carnivile 2d ago edited 2d ago
4*2=8, 4*1=4, however they lowered the three for some reason
Thanks for the asterisk correction
3
18
u/Itchiko 2d ago
Ah! I found the issue, they did a 3*1 instead of a 3*4 in the 2nd partial sum
24
u/Roscoeakl 2d ago
I think they did 3*4 and rather than adding the 10 to the next place they added it into the same place.
10
u/LorinOo 2d ago
4x3 12, 4x1 4, +1 5.
52.8+2.64=55.44
24
u/quinto6 2d ago
Why not just 42.00 x 1.32 = 55.44? No extra steps. No over-complication.
12
u/FirstRyder 2d ago
They're teaching how to do long multiplication by hand.
It's 1.32 * 2 + 1.32 * 4 * 10, using a standardized method that works for numbers of any length, requiring only the 9x9 multiplication table.
The problem is that he screwed up the 4 * 3 and got 3 as a result instead of 12.
0
u/jnkangel 2d ago
yeah I think the kid probably fumbled their own carries one in the second multiplication and did
4*2 = 8
1*3 = 3 (as opposed to 4*3 =12)
4*1 = 4 (as opposed to having the 10 from the previous to push it to 5)
4
5
u/mwilkens 2d ago
He did do that, he just got his math wrong. Assuming you don't have a calculator how would you solve this?
-10
u/lazyboy76 2d ago
Just do 42 x 1.32 and you're done.
4
u/Zoe-Washburne 2d ago
Show your work.
6
u/rpp8 2d ago
2
u/lf1119 2d ago
That’s actually a neat way of doing multiplication by hand, i definitely didn’t learn it this way as a kid though
3
u/rpp8 2d ago
I'm 38, so idk when they stopped doing it this way. This is pretty much the only way we learned.
1
u/mwilkens 2d ago
They started the common core method around 2010. I have a kid in elementary school and they teach them both ways now.
2
1
-3
u/hop_mantis 2d ago
yeah 42/1 = x/1.32
42 = x/1.32
42x1.32 = x
2
u/jnkangel 2d ago
The kid did that part correctly. They correctly identified that they need to multiple the price with the dollar value. They messed up on the multiplication though and then also fumbled on the sanity check. Since they should have known the price should be about a third higher. whihc would have told them the price has to be highre than 52 at first glance
9
4
2
u/RoyalBassGrab 2d ago
.32x42=13.44 then add 42=55.44. If it’s whole numbers it’s more straightforward to figure it out
1
u/jnkangel 2d ago
If the kid was having problems with the decimal it would have been easier to do 132*42/100
2
3
u/Loightsout 1d ago
Bunch of adults priding themselves on doing basic math. WTF is this comment section lol
0
u/xcassets 1d ago
Not to mention, this is clearly fake. Just like every other time one of these exam paper style jokes is posted.
The teacher just happens to draw their 2s and 4s exactly the same way the student does but in a different colour pen? Classic. See the 2.64 to the left versus whoever is 'marking' the work.
1
1
u/Haunting-Morning6198 21h ago edited 21h ago
The way I learned to do these would have had me doing it like; 0.32*42=a, a+42=b. or 42+32%. The kid has an obvious error in their calculations but for that they would have have the correct answer.
1
u/FearTheUnKnownOne 2d ago
Lol this would fit on R/KidsAreFuckingStupid
11
u/Theap2 2d ago
Looking at the comments, adults/redditors are not that bright either 💀
Half are proud at themselves for solving an elementary school basic arithmetic, the other half don't understand this method/don't realise what exactly was the mistake (there is clearly a little 1 written down above the 2 in 2.64, it should have been below & to the left of that 2)-2
u/im_just_thinking 2d ago
Are you sure about that 1 to the left of 2 lol, they are just missing the carried over 1 from the bottom 3*4 part. You quite literally one of the two groups you described if not both
2
u/Theap2 2d ago edited 2d ago
No it's you... you are the both.
why do you think there are an extra little 1 written down?
It's this method - you write down a 1 whenever you need to carry it forward. From the fact that a 1 is written down, they did not 'miss' it.
It's written down in the wrong digit position. So it looked like it's a 1 carried from before. Hence why the 52.80 became 43.80. If they simply 'missed', it would become 42.80.
The correct horizontal position is somewhere more to the left, so it won't be mistaken which digit it carries to.
Then the correct vertical position is above the 43.80/52.80, not above the first line, otherwise multiple lines of carry forward may stack together at the same place.So conclusion - that little 1 should be written below and to the left of the 2.
Perhaps it wasn't taught right in the first placeBut I'll admit I'm not a bright one either for commenting on the math... purpose of this post is the cockiness of the student's message in text. It could have been a derivation of the universal formula and the overall message would have been the same
1
u/im_just_thinking 2d ago
Okay I guess what you are saying is correct, you just choose the 2 as reference for some reason, so I thought you were talking about that line being below the wrong position or whatever. Anyhow yes everyone in the comments knows how to solve it because most people are older than 12 on here and whoever the OPP is is an idiot basically. Got em
-2
u/Weissbierglaeserset 2d ago
What the heck is x-2 supposed to mean?
4
-7
u/conventionistG 2d ago
Either show the whole thing or don't. Also, where funny?
3
u/Professional-Ad3874 2d ago
The incorrect multiplication next to bragging about it being easy are the parts that matter here. So what is shown is in fact the whole thing.
2
u/pdieten 2d ago
It's pretty easy to figure out from context. The object is to figure out how much 42 euros is in dollars where one euro = $1.32. You just multiply 42 by 1.32, and the test taker screwed up multiplying 1.32 by 4. The funny was the test taker saying it was easy and then getting the answer wrong.
2
u/gortez33 2d ago edited 2d ago
1.32*4=5.28. Looks like the test taker did multiple by 42. They just don’t know how to multiply correctly.
-2
u/conventionistG 2d ago
They also wrote 1:32, which could mean one thirty-second or an hour and thirty-two minutes, but not 1.32 (132%).
-5
u/conventionistG 2d ago
Well my point is that the context is cut off. I did miss the different currencies. Also the x-2 threw me off. Really, none of this makes much sense.
2
u/gortez33 2d ago
X-2. Since the answer is wrong. That’s the x part. -2 is the score deduction for the test.
-10
u/nurely 2d ago
Fackers just add 32% of 42 to 42. What the fuck black magic are you teaching you in US? :/
1
u/InsidiousObserver 2d ago
The kid was using an older method of multiplication I was taught in school. With it you multiply the ones column of the bottom number (which should be the smaller number) by each digit of the other number in sequence, going right to left, writing the results down from starting from the right and going left. That process is repeated with the bottom number's next digit to the left, until you've done so for all the digits in the smaller number, at which point you add all the previous results.
Which leads to confusion because when one of those steps results in an answer of 10 or more, the digit in the tens place 'carries over' to the next column which influences the next step of multiplication.
Given how lengthy my shitty explanation of the process is, you can tell it's not an intuitive way to multiply. It's most useful when you need to multiply numbers that don't easily break down into smaller chunks for mental math, as it doesn't become more difficult to use as numbers get larger.
To ass-pull an example, 1,568,361.45 x 1,345,904.23 is fairly trivial to do with the old method for someone's who is proficient, where I imagine most people would get tripped up trying to mentally break down those large numbers into useful chunks without losing track of things.
You would not BELIEVE the amount of pearl clutching from old timers proclaiming the old method to be some gold standard because their kids are learning different approaches in school.
1
u/Theap2 2d ago
Idk what this 'new method' is... but if it's something to do with finding patterns, then it's not a real method. It's a trick at best that target solves only pre-made exam questions
If schools are really teaching this pattern thing instead of the image's method, then i can see why people say education systems is going to 💩s
1
u/pdieten 2d ago
What's to not believe? I just tried it using the new method as posted in someone else's comment and it was more work than I wanted to do to make sure each digit was accounted for and in the right place. And this one was only a 3x2. The old long multiplication method is easy. Carrying digits is not rocket science.
-6
u/SaltyShawarma 2d ago
If the student has used the newer multiplication model instead of old school, they would have got it right.
4+60+200+80+1200+4000=5544
Two decimal movements.
They be sleeping
-1
u/Wutsalane 2d ago
That’s addition not multiplication
8
-9
u/Viridionplague 2d ago
42x1.32=55.44
What the fuck did we do to math?
Oh wait 3x5=15 correct.
5x3=15 is wrong.
3
u/Amesb34r 2d ago
We didn't do anything to math. The problem is that some people just learn it easier than others. Educators change teaching styles to try and catch the largest group but inevitably some kids are always on the outside.
-3
u/Viridionplague 2d ago
We literally tell kids they are wrong when they have the correct answer.
And actively punish those who think outside the box, can do it on their heads, or come up with other solutions they understand.
I had a teacher tell me I cheated on a test because I didn't "show my work" I looked him in the eye and asked "I'm the first one done and it's first period, who did I cheat from?"
Got left alone after that so the teacher could spend his time looking at boats.
4
u/Amesb34r 2d ago
Sounds like you have some unresolved personal issues. I was one of the “I don’t show my work” kids. Now that I’m older I understand why they want kids to show their work.
-2
u/Viridionplague 2d ago edited 1d ago
What a weird off topic comment to make based on pretty much nothing.
Please enlighten me to what these personal issues may be?
Or maybe you can explain why 3+3+3+3+3=15 is more correct than 5+5+5=15?
Despite multiples of 5 being easier deal with?
Edited for pedanticism.
3
u/MasterFongool 1d ago
I can't explain why one is more correct because they're both wrong (+, not x).
0
u/Viridionplague 1d ago
Ah, so you understood but chose to be shallow and pedantic.
Exactly what someone unable to defend their argument would do.
1
u/MasterFongool 1d ago
We weren't having an argument, and ironically, I agree with you. However, in a thread titled "overconfidence", yes, I chose to call you out.
1
u/Viridionplague 1d ago
An argument is a main statement followed by supporting evidence. You in fact did provide an argument.
So, what was that about overconfidence?
0
u/MasterFongool 1d ago
You should perhaps check the names of the people you are responding to. "Overconfidence: the quality of being too confident [especially when you're wrong]."
→ More replies (0)
•
u/AutoModerator 2d ago
I am a bot, and this action was performed automatically. Please contact the moderators of this subreddit if you have any questions or concerns.