DRDO Multi tasking staff Model paper 9

We know,
Average of quantities = sum of all quantities/no. of quantities
The mean of marks secured by 60 students in division A of class X is 64
Total marks secured by 60 students in division A of class X = 64 × 60 = 3840
The mean of marks secured by 40 students in division B of class X is 60
Total marks secured by 40 students in division B of class X = 60 × 40 = 2400
The mean of marks secured by 60 students in division C of class X is 58
Total marks secured by 60 students in division C of class X = 58 × 60 = 3480
Total no. of students in three division of class X = 60 + 40 + 60 = 160
Total marks secured by 160 students = 3840 + 2400 + 3480 = 9720
∴ Mean of marks of the students of three divisions of Class X = 9720/160 = 60.75