So I'm having a little trouble with 7th gr math

I’m trying to help my son with:

ans = 3/m + 8/m’

The answer in the book is 11/m

Now, I’ve only got 2 degrees, so I’m sure I’m wrong, but notice the “prime” (’) at the second “m”?

How come it’s treated as “m” in this problem? What have I forgotten? Shouldn’t m’ = 1/m?

So isn’t the problem really ans = 3/m + (8/(1/m))?
ans = 3/m + 8m

Why can’t I do 7th grade math?

Typo or printer’s error, maybe?


But is m’ the inverse of m?

m^-1 is the inverse. m’ = 1, IIRC. Still doesn’t make the book answer right, though.

Isn’t that awful when you can’t do some of the math these kids are getting these days? I was trying to help a fifth grader with her math the other day and couldn’t do this crazy “new math” stuff. I felt incredibly stupid. I’m a high school senior, for crying out loud. I got a B in precalculus. And I can’t do fifth grade math???

I’ve never heard of m’ meaning 1/m. (m[sup]-1[/sup] would be 1/m).

m’ could mean the derivative of m with respect to some variable. (If it’s the derivative of m with respect to m, then it would be 1.) However, that wouldn’t be the case for seventh grade math.

m’ could also just be a different variable. In physics, we sometimes use m for mass, and if there are two different masses in the problem, then we might label one m and the other m’.

So, I see too possibilities:
(1) There are two variables in the problem, m and m’. And some other information is given which leads you to discover that m = m’.
(2) It’s just a typo, and it should be an m.

If the entire problem is what you stated in the OP, then I’d say it has to be a typo.

Ask an 8th grader. :slight_smile:

That’s exactly how I feel. I was even embarassed to post this question. I know it’s the same concepts, but it’s a new language, and that’s what’s frustrating me.

tim Arrrrgh m[sup]-1[/sup] is the inverse!!! I really am stupid!!

The only other info is that m and m’ <> 0
which explicitly states m’, so I don’t hink it’s a typo.
Maxx It’s after dark. I’m not allowed to talk to them.

You know, after re-re-re-reading the problem and others like it, they infer that m = m’

By “infer”, I mean that there is no info given. They just seem to treat them as the same value. Isn’t that screwed up? In every case, if you treat “m” as m’ or “a” as a’, the answer is what is given in the “Answers to Selected Questions” in the back of the book.

No wonder kids think math is hard. If they’d state things clearly, it would be a lot easier.

Is there more to the problem? Is it part of a series of problems? Is there some set up or something? A picture? Is it part of a word problem?

Because (if I remember fractions right)
3/m+8/m’= (3m’+8m)/(mm’)

their answer is right if m=m’ (or if m=m’=1) - but we don’t really know…