The average weight of some students in a class was 60.5 kg. When 8 students, whose average weight was 65 kg, joined the class, then the average weight of all the students increased by 0.9 kg. The number of students in the class,initially, was:

32

Lets assume earlier total number of student = x

Sum of weights of student = 60.5x

Now total number of student = x + 8

Total weight increased = 8 x 65 = 520

As per question

(X + 8) x (60.5 + .9) = 60.5x +520

x= 32

So initial no. of student = 32

So, initial  total number of student were 46