Thread: Averages

I have a problem that I've been working on FOREVER! I cannot use Algebra or anything like Trig or Calculus to solve it. I have to describe it in it's basic form. By trial and error, I think the answer is 20, but I'm also not allowed to use trial and error (guess and check). How in the world can it be solved without Algebra?

3. Two algebra classes took the same exam. The mean grade for the first class was 88. The second class had a mean grade of 79. The mean grade of the two classes combined was 84. If there were 25 students in the first class, how many were in the second class?

Consider these two equations

and

where x is the summed scores of students in class 2 and n is the number of students in class 2.

But if the answer is 20, how would I describe it not using Algebra? That's what's stumping me.

Originally Posted by mswanson502

But if the answer is 20, how would I describe it not using Algebra? That's what's stumping me.

You're meant to use algebra! And post #2 tells you the two equations to solve simultaneously. The answer to the question will be the value of n (which is 20).

We were told in our instructions that we were not allowed to use Algebra or Trial and Error. I get what you're doing though. That does help. I just need to figure out how to explain it by taking the Algebra out. This is a college course to learn how to teach math to Elementary students who wouldn't know Algebra. Frustrating!