The midpoint of 85 and 90 is 87
If the quiz is worth 50 points and each question is worth 10 that means for every question he could’ve missed would be taking away 10 from that 50. So lets say if he misses 2 questions. 2 x 10 would be 20. You take away 20 from 50 which would be: 50 - 20 = 30. And it goes on from there.
Hope that helps!
