Wrong answer = x
Correct answer = y
Total questions: x+y = 30
Rewrite for x: x = 30-y
Total points:
-8x + 7y = 0
replace x with 30-y
-8(30-y) + 7y = 0
Simplify:
-240 + 8y + 7y = 0
Combine like terms:
-240 + 15y = 0
Add 240 to each side:
15y = 240
Divide both sides by 15:
y = 240 / 15
y = 16
There were 16 correct answers
30-16 = 14 wrong answers.
