Question

In a class of $100$ students there are $70$ boys whose average marks in a subject is $75$. If the average mark of the complete class is $72$, then the average marks of the girls is

• A. $65$
• B. $68$
• C. $70$
• D. $71$

Answer 1

The correct option is A $65$

Here, $n_b\overline{x_b}+n_g\overline{x_g}=n\overline{x}$
where, $n_b=70,\overline{x_b}=75,n_g=30,\overline{x}=72$

$\therefore$ Average marks of girls $=\frac{100\times 72-70\times 75}{30}=\frac{7200-5250}{30}=65$