Question

The mean weight of $60kg$ students in a class is $40kg$. The mean weight of boys is $50kg$ while that of girls is $30kg$. Find the numbers of boys and girls in the class.

Answer 1

Let $x$ be the total weight of all the students.

It is given that mean weight of $60$ students is $40$ kg.

So,

$\frac{x}{60}=40$

$x=2400$

Let $y$ be the number of boys in the class.

The mean weight of boys is given as $50$.

The total weight of boys is $50y$.

The mean weight of girls is given as 30. The total weight of girls will be $30\left(60-y\right)$.

So,

$2400=50y+30\left(60-y\right)$

$2400=50y+1800-30y$

$600=20y$

$y=30$

Then, $60-y=60-30=30$

Therefore, the number of boys is $30$ and the number of girls is $30$.