# The mean weight of 60 students of a class is 40kg. The mean weight of boys is 50kg , while that of girls is 30kg. Find the number of boys and girls in the class.

1
by p6riyanannerva

2016-03-17T16:34:25+05:30

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Let the no. of boys = x
no. of girls = 60-x

A/Q,
mean weight of boys = 50 kg
Total weight  of boys ÷ x = 50
⇒ total weight of boys = 50x

And,
mean weight of girls = 30 kg

Total weight  of girls ÷ (60-x) = 30
⇒  Total weight of girls = 30(60-x) =1800 - 30x
now,
mean weight of 60 students = 40 kg
(Weight of girls + Weight of boys) ÷  total no. of students = 40
⇒   (1800 -30x + 50x) ÷ 60 =40
⇒   1800 + 20x =40 ×60
⇒    20x = 2400 - 1800
⇒    20x = 600
x = 600/20 = 30
Therefore total no. of boys = 30
and total no of girls = 60 - 30 = 30
Therefore,
No. of Boys =30
No. of Girls = 30