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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
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