Question

The mean weight of 80 students in a class in 56.25 kg. The mean weight of
boys in the class is 60 kg. and that of the girls is 50 kg. Find out the number
of boys and the girls in the class.
​

Answer 1

Given :- The mean weight of 80 students in a class in 56.25 kg. The mean weight of boys in the class is 60 kg. and that of the girls is 50 kg. Find out the number of boys and the girls in the class. ?

Solution :-

Let us assume that, the number of boys in class are x and number of girls in class are y .

So,

→ No. of boys + No. of girls = Total students in class

→ x + y = 80 -------- Eqn.(1)

Now,

→ Mean weight of 80 students = 56.25 kg .

then,

→ Total weight of class = 80 * 56.25 = 4500 kg .

and,

→ Mean weight of boys = 60 kg.

→ Total weight of boys = 60 * x = 60x kg .

and,

→ Mean weight of girls = 50 kg.

→ Total weight of girls = 50 * y = 50y kg .

So,

→ Total weight of boys + Total weight of girls = Total weight of class

→ 60x + 50y = 4500

→ 6x + 5y = 450 ------------ Eqn.(2)

Multiply Eqn.(1) by 5 and subtracting from Eqn.(2), we get,

→ (6x + 5y) - 5(x + y) = 450 - 5*80

→ 6x - 5x + 5y - 5y = 450 - 400

→ x = 50 .

Putting value of x in Eqn.(1) ,

→ 50 + y = 80

→ y = 80 - 50

→ y = 30 .

Hence, the number of boys and the girls in the class are 50 and 30 respectively .

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