Question

A boy gets 3 marks for each correct sum and loses 2 marks for each incorrect sum. He does 24 sums and obtains 37 marks. What was the number of correct sums ?

Answer 1

Let number of answers which he made correct be x and the number of answers which he made incorrect be y.
thereofre
x + y = 24...(1)
Since he gets 3 marks for correct answer and loses 2 marks for incrorrect answer. total scored marks = 37.
3x - 2y = 37....(2)
Multiplying eq(1) by 2 and adding to eq (2):
2x + 2y = 48
3x - 2y = 37
5x = 85
$x=\frac{85}{5}=17$