MATH
posted by KIM .
An arithmetic student needs at least a 70% average to receive credit for the course. If she scored 86%, 77%, and 64% on the first three exams, what is the lowest score she can get on the fourth exam to receive credit for the course?

0.7 * 400 = 280
She has 86 + 77 + 64 = 227
280  227 = 53