Assume that the original number of students in grade five is X, which is deduced from the meaning of the question:

(x+ 15×2+ 10)×37.5% = x- 10，

(x+40)×37.5%=x- 10，

? 37.5%x+ 15=x- 10，

0.625x=25，

x = 40

40+ 15×2=70 (person);

A: There are 40 students in grade five and 70 students in grade six.