Question

Mean weight of a class is $50Kg$. Mean weight of boys and girls are $52Kg$ and $42Kg$ respectively.
Find the ratio of number of boys and girls in the school.

• A. $5:1$
• B. $4:1$
• C. $3:2$
• D. $3:5$

Answer 1

The correct option is B $4:1$

$u_g=42$, $u_b=52$, $u=50$
Assume the total strength of class to be 100.
So, $n_b=n$ and $n_g=100-n$
$u=\frac{u_g\times n_g+u_b\times n_b}{n_g+n_b}$
$\therefore 50=\frac{42\times (100-n)+52\times n}{100}$
$\therefore 50=\frac{52n+4200-42n}{100}$
$\therefore 800=10n$
Thus, $n=80$ and $100-n=20$
Hence the ratio : $(4:1)$
Ans-Option B.