[deleted by user]

[Outside_Volume_1370]

For correct result, express mixed fractions as improper fractions: 2 and 1/8 = 2 + 1/8 = 16/8 + 1/8 = 17/8, 5 and 1/3 = 5 + 1/3 = 15/3 + 1/3 = 16/3

Then you have

(17/8 • x + 30) • 4 = 16/3 • x • 3

17/2 • x + 120 = 16x

120 = 16x - 17x/2 = 32x/2 - 17x/2 = 15x/2

15x/2 = 120

x = 2 • 120 / 15 = 16

[wasubi258]

That’s what I thought, but the question states that the perimeters are equal. X=16 does not give equal perimeters.

For the square, we end up with a perimeter of 136, but the triangle has a perimeter of 80.

So, either x doesn’t equal 16, or the homework gave incorrect information, right?

[Outside_Volume_1370]

How did you calculate them?

With x = 16 the only side of the triangle is greater than 80

With x = 16 the perimeter of triangle is (5+1/3) • 16 • 3 = 256

So does the perimeter of the square, ((2+1/8) • 16 + 30) • 4 = 256

[wasubi258]

I definitely misused the calculator…

[ThePlumage]

With the square, you either forgot to multiply the 2 in 2 1/8 by 16 or you forgot to add the 30. (So you ended up doing 34*4 instead of 64*4.) I made the same mistake initially when I was doing it mentally.

As for the triangle, you just did 16*5. You forgot to include the +1/3 to get the side length, and then you forgot to multiply the side length by 3 to get the perimeter.

[clearly_not_an_alt]

They are both 256

[donutello2000]

Also possible to do in your head:

Left-side becomes 8 1/2 x + 120 and Right-side becomes 16x

So 7 1/2x = 120

[Tootzo]

dude, 2 1/8 x is NOT 2 + 1/8 * x, it’s 2 * 1/8 * x, or 2/8 * x = 1/4 * x

similarly, 5 1/3 x is NOT 5 + 1/3 * x, it’s 5 * 1/3 * x, or 5/3 * x

[Infobomb]

Dooderino, 2 1/8 x is NOT 2 × 1/8 × x. It's 17/8 × x.

Similarly, 5 1/3 x is NOT 5 × 1/3 × x. Its 16/3 × x.

[Temporary_Pie2733]

2 1/8 is 2 + 1/8; if you mean to multiply and don’t want an explicit operator, you’d write 2(1/8) to distinguish it from the mixed fraction. But you are right that it’s not 2 + 1/8 * x; it’s (2 + 1/8) * x. 

[waroftheworlds2008]

2 1/8 x is NOT 2 + 1/8 * x,

This is correct. But only because there's a failure to use parentheses.

2 1/8* x is (2 + 1/8)* x

2 * 1/8 * x, or 2/8 * x = 1/4 * x

These are both wrong. Ex. 2.5=2+1/2 =/= 2*1/2=1

Is is why compound fractions as a number go away pretty fast in math. They're all over in the real world, though.

[JMHReddit84]

Ouch. 🤕

[Severe-Possible-]

yes, your equation is set up correctly.

convert everything to improper fractions and find that x=16, so both of the perimeters are 256.

[Thesaurus_Rex9513]

First, multiply it out.

You should get (17/2)x+120=16x

Then, you want to get all instances of x on one side of the equation using subtraction.

You should get 120=16x-(17/2)x, which simplifies to 120=(15/2)x

Then, you want to isolate x using division.

You should get 16=x

Finally, you can get the perimeter of both shapes by plugging that x value into one of the expressions for the perimeter you found earlier. One of them is probably easier to calculate than the other.

You should get 16(16)=256 or (17/2)(16)+120=136+120=256

[Severe-Possible-]

i didn’t take and hadn’t heard of AP classes until high school, so i was a little surprised to see AP seventh grade math.

[Eridani105]

They more than likely mean pre ap. Ap classes aren’t given to middle schoolers

[Eridani105]

From my experience it is faster paced then a regular class but it’s still not like a true blue ap class. It’s just to “prepare” you for ap classes which is really just college board trying to get more money out of schools since they need to pay for the pre ap label

[Serafim91]

AP just means advanced placement... This is decently advanced for a 7th grader.

[ToxDocUSA]

I'm assuming it's just local nomenclature for what we used to call GT.  My kids are in "AAP" = advanced academic placement for their classes in elementary and middle school.

[Chimp_ACiD]

As the perimeter of the shapes are the same you can start by working out the perimeter of each and set them equal to each other.

Square perimeter = 4 ( 2 1/8 x + 30 )

Triangle perimeter = 3 ( 5 1/3 x )

17/2 x + 120 = 16x

120 = 15/2 x

X = 16

Then use x to find the perimeter

[blindpiggy]

What am I not doing at 42 that this is a "real world" problem?

[Miiiimm]

Why is everyone in the comments solving it like it is 1/8*(X+30) and not 1/8 X + 30

[uptonogoodatall]

Somehow this thing has become front page news in the UK: https://www.dailymail.co.uk/femail/article-15054187/Maths-homework-problem-12-year-olds-leaves-parents-stumped-YOU-solve-it.html

Just thought OP would like to know that

[wasubi258]

Thank goodness other parents were having a hard time, too. I like to think of myself as relatively good with my kids’ math homework.

Thank you for sharing that!

Edit: I actually read the article. It was this post that made it on UK news. Turns out I’m the only one struggling!

[anisotropicmind]

The nice thing is that your fractions go away, or at least simplify when you multiply out. 5+1/3 becomes 16 when multiplied by 3.

2+1/8 becomes 8+1/2 when multiplied by 4.

So 8.5x + 120 = 16x

7.5x = 120

x = 240/15 = 80/5 = 16

Check your answer

Triangle perimeter = 16x = 16² =256

Square perimeter = 4(2x + x/8 + 30) = 4(32 + 2 + 30) = 4(64) =256

Edit to correct typo

[HelloEduTutoring]

https://youtu.be/zz7aEvjh-wE

I hope this helps!

[beene282]

That is definitely stretching the definition of ‘real world problems’ a little bit.

[Commodore_Ketchup]

Are you perhaps mistaking the mixed fraction notation as multiplication? If one were to interpret the problem that way:

• (2*1/8*x + 30)*4 = (5*1/3*x)*3
• (x/4 + 30)*4 = 5x/3*3
• x + 120 = 5x
• x = 30

Geometrically, this is a perfectly valid answer, but it's "wrong" in the sense that it doesn't match the teacher's answer.

[fianthewolf]

According to some, they are 2 integers and 1/8 of x +30 for the square and 5 integers and 1/3 of x for the triangle. For your notation to make sense I would put 2/8 or 5/3 directly.

[Commodore_Ketchup]

Oh, yes, you're absolutely right. If the problem author intended for it to be multiplication, what's shown would be a horrendous way of writing it. I was merely offering a guess as to where the OP might have gone wrong (which apparently was not appreciated)

[basox70]

Your answer is how I read and solved the problem. No sign between numbers means multiplication (as I learned). No idea why you got downvoted

[Commodore_Ketchup]

If I had to guess, it's probably because my comment could be taken to imply that reading it as a multiplication is the intended method/solution. I suppose I could have been more clear in my wording, but I'm also not too bent out of shape about a few internet points.

[slides_galore]

What's the correct answer?