Answers

2015-09-24T21:28:03+05:30
Total students in class = 150
mean weight = 60 kg
total weight = 150×60 = 9000 kg

Let the total number of boys = x
mean weight of boys = 70kg
total weight of boys = 70×x = 70x kg

total number of girls = total students - no. of boys = 150 - x
mean weight of girls= 55kg
total weight of girls = 55×(150-x) = 55×150 - 55x = (8250 - 55x) kg

Total weight = weight of boys + weight of girls
⇒ 9000 = 70x + (8250 - 55x)
⇒ 9000 = 70x + 8250 - 55x
⇒ 9000 - 8250 = 70x - 55x
⇒ 750 = 15x
⇒ x = 750/15 
⇒ x = 50

So number of boys = 50
number of girls = 150 - 50 = 100

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