Question

The mean weight of 150 students is 60kg. The mean weight of boys is 70kg and standard deviation is 10kg. For girls mean weight is 55kg and standard deviation is 15kg. Find out the no. of boys and girls. Find out combined standard deviation

Answer 1

Let the number of boys be 'x'

and girls in the school be 'y'

Therefore x + y = 150 (given)

Since, Mean =





⇒

[Taking 5 common from both the sides]

Now we have two equations

1st: 14x + 11y =1800

2nd: x + y =150

Multiplying 2nd eq by 11 and simultaneous solving, we get

14x + 11y = 1800

11x + 11y = 1650

By subtracting y terms will be cancelled

⇒3x = 150 OR x = 50 Hence y = 150 - 50 = 100
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