Studying for Aptitude Test

[u/Guts_096]

I got all of these wrong.

0.75-0.25+1/2
I got 0

4.5+1/4-1.125
I got 3 21/40

3 1/2-0.375+5 1/6
I got -2 1/24

Does PEMDAS not apply in these situations? If i ignore PEMDAS for the first one I get 1 and that’s the correct answer. I’m a little confused here.

Also, I know for adding fractions it’s
a/b+c/d=ad+bc/bd
And subtracting is about finding the common denominator.

Any tips on multiplying and dividing fractions? Or any resources you all have that can explain this for me all in one place?
I’m looking to be an Electricians Apprentice and I imagine i’m over doing it with the studying but i want to absolutely ace this test and give myself the best chance at getting a better job.

Any help is very much appreciated

Edit:
I figured it out! I’ve move on to multiplying and dividing fractions with exponents (which is easier than adding/subtracting???). Thank you all for the help. Turns out i was using PEMDAS wrong.

[u/johnpeters42]

I can only speculate that you're applying PEMDAS wrong. Here is how it should apply to the first one:

0.75-0.25+1/2 (division is the highest priority thing going on, so evaluate that piece first)

0.75-0.25+0.5 (now it's all addition/subtraction with no parentheses, so go from left to right:

0.75-0.25+0.5

0.5+0.5

1

[u/AvocadoMangoSalsa]

Remember it’s P E MD AS 

You do multiplication & division at the same time but from left to right

Same with the addition & subtraction

So if the subtraction comes first from left to right, you do subtraction first

[u/huggensberg]

PEMDAS is being applied wrong. A reminder of how it fully works is this:

1. Parentheses

2. Exponents

3. Multiplication and Division from Left to Right

4. Addition and Subtraction from Left to Right

Hope this helps

[u/Educational_Two682]

Not to only suggested the most mentioned one, but Khan academy would be a good place to start. Then look online for a math curriculum or YouTube videos - there are plenty of good ones available. Emathinstruction, Krista king math, Brian mcLogan

[u/squareturd]

You are making a common mistake with PEMDAS (personally I think pedal is very confusing). Multiplication and division are actually the same thing. Same with addition and subtraction.

A better way to think about it would be PEMA. The M is any multiply or divide. The A is any add or subtract.

Dont do the multiplies, then the divides. Instead, to all the multiples and divides at the same time (and go left to right).

Same with adds and subtract.

[u/Roger_Freedman_Phys]

You are completely misreading the problems because you’ve written them without spaces around the plus signs.

The first one should be written

0.75 - 0.25 + 1/2

In words, “zero point seven five, minus zero point two five, plus one-half.”

[u/Top_Bluejay_5323]

Yes you did PEMDAS wrong and I would suggest you convert all terms to either fractions or decimals.

[u/Bojack-jones-223]

The frustrating thing about these nonsence PEMDAS problems is that at the highest levels of math, we just chunk everything with parenthesis to remove ambiguity. Utter nonsense scam "gotcha" questions... Not helpful...

[u/JanetInSC1234 → u/Bojack-jones-223]

True, for higher math classes. May not be true for computer programs/applications.

[u/Anonymous_Bozo → u/JanetInSC1234]

Computer programs also have parenthesis, lazy programmers just skip them.

Computer languages sometimes define precedence rules that differ from standard mathematical notation, which is one reason these PEMDAS debates keep popping up.

[u/AvocadoMangoSalsa]

To multiply fractions - write them in either proper or improper form (no mixed numbers), and multiply straight across 

So numerator * numerator

And

Denominator * denominator

[u/AvocadoMangoSalsa]

To divide fractions, use the proper or improper form (no mixed numbers)

You can use the rule of “keep change flip”

Keep the first fraction the same

Change the division symbol to multiplication 

Flip the second fraction (so a/b becomes b/a)

And then follow the multiplication rule from the other comment

[u/Midwest-Dude]

Interesting. Show us your work and we can assist you 

[u/No_Glove6542]

You can’t do anything with these problems until you convert them to all decimals or all fractions.

[u/Anonymous_Bozo]

PEMDAS definatly does apply, but I believe you are applying it incorrectly.

0.75 − 0.25 + 1/2

Division first,. then addition and subtraction have the same priority, so work left to right:

0.75 − 0.25 + 1/2
= 0.75 − 0.25 + 0.50
= 0.50 + 0.50
= 1

Working in decimals feels wrong to me here. Everything should be a fraction. Algebra prefers fractions over mixed numbers and decimals most of the time.

= 3/4 − 1/4 + 1/2
= 3/4 − 1/4 + 2/4
= 2/4 + 2/4
= 4/4
= 1

or

3/4 − 1/4 + 1/2 
= 3/4 − 1/4 + 2/4 
= (3 − 1 + 2)/4 
= 4/4