Algebra homework

Question

A math quiz consists of 30 questions. The first 20 questions are worth 4 points each. The last 10 questions are worth 7 points each. No points will be deducted for each wrong answer. Justin scores 124 points on the math quiz. How many of the first 30 questions and how many of the last 20 questions does he answer incorrectly?


I'm trying to form 2 equations:
4x + 7y = 26 (150-124)

But I need to form another equation but I don't know how. Please help!!!
Thanks！

Gloria

Answer 1

4x + 7y = 124

4(20) =80 + 7(6) = 122. Nope

7(8) = 56 + 4(17) = 124 Yes

8 correct on 7 pointers, 2 incorrect

17 correct on 4 pointers. 3 incorrect

y has to be an even number, x can be either even or odd

maybe there's other solutions? Nope.

7(10) = 70 + 54 but 4 doesn't divide 54.

can't go above 10, as that's the maximum number possible for 7 pointers