Question

The mean weight of $150$ students in a certain class is$60$ kg. The mean weight of boys in the class is $70$ kg. and that of the girls is$55$kg., the ratio of boys and girls respectively is

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

Answer 1

The correct option is B $1:2$

Let number of boys is $n_1$ and number of girls be $n_2$
Given total number of students is 150. $\Rightarrow n_1+n_2=150$ (i)
Now mean weight of total students is $=\frac{70n_1+55n_2}{150}=60$ (given)
$\Rightarrow 14n_1+11n_2=1800$ (ii)
Solving (i) and (ii) we get $n_1=50,n_2=100\therefore n_1:n_2=1:2$