Question

answer with explanation

Answer 1

Let number of boys in the class be 'x'.

Then number of girls will be 150-x.

Now mean weight ====> Arthimetic weight of boys and girls.

Given A.M of boys is 70kg. ====> Sum of weights of boys/x = 70

===> Sum of weights of boys is 70x.

A.M of girls is 55kg. ====> Sum of weight of girls/150-x = 55

====> Sum of weights of girls is 55(150-x).

A.m of weights of class is 60kg ====> Sum of weights of all the students/ 150= 60 ====> Sum of weights of all the students is 150 x 60 = 9000.

Sum of weighhts of all students is Sum of weights of boys + sum of weights of girls.

====> 9000=70x+55(150-x)

===> 9000= 70x + 8250 - 55x

=====> 9000 - 8250 = 15x

=====> 750 = 15x ===> x = 50

Num of boys is 50 and girls is 100.