The number of students in classes A and B are 60 and 70, respectively. The average score in mathematics of students in class  B is 57 and that of all students in classes A and B is 63. What is the average score of students in class A?

Given that the average score of students in class B is 57

and no. of students in class B is 70

therefore,sum of total marks of students in class B is 70$$\times\ $$57=3990.

Given that the average score of all students in classes A and B is 63

i.e;total sum of scores/130 =63

sum of scores in A and B =8190

to know the average score in class A = (8190-3990)/60 = 4200/60 (60 since number of students in class A is 60)

i.e;70

hence answer is 70