Question

The mean weight of $60$ student in a class is $40$kg. The mean weight of boys is $50$kg while that of girls is $30kg$. find the number of boys and girls in the class.

Answer 1

Let $x$ be the number of boys, then the number of girls will be $\left(60-x\right)$.

The mean weight of boys is 50 kg, then the total weight of boys will be, $50x$.

The mean weight of girls is 30 kg, then the total weight of girls will be $30\left(60-x\right)=1800-30x$.

The mean weight of 60 students is 40 kg, so

$\frac{weightofgirls+weightofboys}{totalno.ofstudents}=40$

$\frac{1800-30x+50x}{60}=40$

$x=\frac{600}{20}$

$x=30$

So, the number of boys is 30 and the number of girls is $\left(60-30\right)=30$.