A math student has solved 500 problems and got 350 of them right.
If he now starts getting every problem right, after how many problems will he have got 75% of all his problems right?
+130071 Call x the number of consecutive problems (after 350) that he needs to solve
So
(350 + x) /(500 + x) = .75 cross-multiply
350 + x = .75 ( 500 + x) simplify
350 + x = 375 + .75x
x - .75x = 375 - 350
.25x = 25
x =25 /.25 = 100
He will have 75% right after 350 + 100 = 450 problems
