Question

In a class the average weight of 60 boys is 64 kgs and that of 75 girls is 70 kg. After a few days, 60 %of the girls and 35 % of the boys leave. What would be the new average weight of the class (in kgs). Assume that the average weight of the boys and the girls remains constant throughout.

Answer 1

Let initial no. Of students=x
Avg. Wt. = 60kg
Therefore, total wt. = 60x

Again,
No. Of students= 8
Avg. Wt. = 64kg
Therefore, total wt.= 64*8=512kg

Now, total avg. Wt.=62kg
Total students= x+8
Therefore, total wt. =62*(x+8) = 62x + 496

A/Q
60x + 512= 62x+496
-› 512-496 = 62x - 60x
-›2x=16
-› x =16/2 = 8

Therefore, initial no. Of students=x=8

Answer 2

Let initial no. Of students=x
Avg. Wt. = 60kg
Therefore, total wt. = 60x

Again,
No. Of students= 8
Avg. Wt. = 64kg
Therefore, total wt.= 64*8=512kg

Now, total avg. Wt.=62kg
Total students= x+8
Therefore, total wt. =62*(x+8) = 62x + 496

A/Q
60x + 512= 62x+496
-› 512-496 = 62x - 60x
-›2x=16
-› x =16/2 = 8

Therefore, initial no. Of students=x=8