The average weight of 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 total number of students now in the class is:

Let the initial number of students in the class be x.
Initial average weight = 60.5kg
Total initial weight = 60.5xkg

Weight of 8 new students = 8×65=520kg

Total number of students now = x+8
New average weight = 60.5+0.9=61.4kg

According to the question:

x+8
60.5x+520
​
=61.4
60.5x+520=61.4(x+8)
60.5x+520=61.4x+491.2
520−491.2=61.4x−60.5x
28.8=0.9x
x=
0.9
28.8
​
=32
The initial number of students was 32.
The total number of students now in the class = 32+8=40.