Question

# In a class of 48 students the number of girls is three-fifth then the number of boys. The number of boys isA. 25B. 30C. 35D. 48

Hint: The total class can be written as sum of number of boys and girls or it can be represented as,
$\text{Number of boys }+\text{ Number of girls }=\text{ 48}$.
Now as we know the number of girls is $\dfrac{3}{5}$ of the number of boys so substitute it and hence find the number of boys.

In the question we are told that in a class of 48 students the number of girls is three-fifth then the number of boys. So, we have to find a number of boys.
So, we can write according to the question,
$\text{Number of girls}=\dfrac{3}{5}\times \text{ number of boys}\text{.}$
As we know that total strength of class which is 48. So we can also tell that the number of boys + number of boys is equal to 48.
Now we know that the number of girls is equal to $\left( \dfrac{3}{5} \right)$ times the number of boys. So we can use it as,
Number of boy’s $+\dfrac{3}{5}$ number of boys
$\Rightarrow \text{number of boys}\left\{ 1+\dfrac{3}{5} \right\}$
$\Rightarrow \text{number of boys}\times \dfrac{8}{5}$
Now we can say that the number of boys $\times \dfrac{8}{5}$ can be written as 48.
So,
$\dfrac{8}{5}\times number\text{ of boys=48}$
we can also write,
$Number\text{ of boys=48}\times \dfrac{8}{5}$
Now on simplification we can say that the number of boys is 30.
Hence, the correct option is 'B'.

Note: We can take the number of boys as x. So, the number of girls will be $\dfrac{3x}{5}$ hence, we can write $x+\dfrac{3x}{5}=48$ and then solve for x to get the answer.