Question

The ratio of number of boys to girls in a class is 1 : 25. If 36 more girls join, the ratio becomes 1 : 28. The number of boys in class is

• A. 24
• B. 32
• C. 12
• D. 48

Answer 1

The correct option is C 12

Consider number of boys in class be b and number of girls in class be g.

So, $\frac{b}{g}=\frac{1}{25}$. - (1)

If 36 more girls join, the ratio becomes $\frac{1}{28}$

i.e., $\frac{b}{g+36}=\frac{1}{28}$. - (2)

Divide equation 1 by 2, we get,

$\frac{b}{g}÷\frac{b}{g+36}=\frac{1}{25}÷\frac{1}{28}$.

$\frac{g+36}{g}=\frac{28}{25}$

cross multipying we get,

$\frac{g+36}{g}=\frac{28}{25}$

$25g+(36\times 25)=28g$

$900=3g$

$g=300$

300 is the number of girls, substituting the value of girls in equation (1) we get

$\frac{b}{300}=\frac{1}{25}$

number of boys = 12.