(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.