Question

In a group of students, the mean weight of boys is $65$ kg. and mean weight of girls is $55$ kg. If the mean weight of all students of group is $61$ kg, then the ratio of the number of boys and girls in the group is

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

Answer 1

Answer: (C)

3 : 2

Let the no. of boys and girls are $n_1$ and $n_2$ respectively.
Mean weight $=\frac{n_1{w}_1+n_2{w}_2}{n_1+n_2}$
$\Rightarrow \frac{65n_1+55n_2}{n_1+n_2}=61$
$\Rightarrow 4n_1=6n_2$
$\Rightarrow n_1:n_2=3:2$