Question

The total number of students in a school was $660$. The ratio between boys and girls was $13:9$. After some days, $30$ girls joined the school and some boys left the school and new ratio between boys and girls become $6:5$. The number of boys who left the school is

• A. $50$
• B. $40$
• C. $30$
• D. $60$

Answer 1

Answer: (C)

$30$

In the first case
Number of boys $=660\times \frac{13}{22}=390$
Number of girls $=660\times \frac{9}{22}=270$
Let the number of boys who left the school be $x$.
According to the question,
$\Rightarrow \frac{390-x}{270+30}=\frac{6}{5}$
$390-x=360$
$x=390-360=30$.