Question

the mean weight of 150 students in a class is 60 kg. the mean weight of boys is 70 kg while that of girl is 55 kg. find the number of boys and girls in the class. ​

Answer 1

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Answer 2

SOLUTION

Let the number of boys be x

Let the number of boys be x& girls in the school be y

Therefore x+y = 150 (Given)

Since, mean

=) Sum of observations/Total number of observations

$= > \frac{(70 \times x) + (55 \times y)}{x + y} = 60$

=) 70x+55y= 60×150

=) 70x+55y= 9000

=) 14x+ 11y= 1800 [taking 5 common both sides]

Now, we have 2 equations

14x+ 11y= 1800.............(1)

x+ y= 150..........(2)

Multiplying (2) by (1) and simulataneous solving, we get

=) 14x+ 11y= 1800

=) 11x+ 11y= 1650

By subtracting y terms will be cancelled

=) 3x= 150

=) x= 150/3

=) x= 50

hence,

y= 150 -50

=) y= 100

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