Answer:14
Explanation:
figure out 5x20,, which gives you 100 points
use trial and error is my method :)
if he answered 10 correct, he would get 50 points and lose 10. this gives 40 points. its an error
we now know its between 11 right and 19 right
we continue to do this till we get it right
14 x 5 = 68. - 4 makes 64.