Question

$25\%$ of the students in a class are girls. What percentage of students are boys? If the number of boys in that class is $30$. Find the total number of students in that class.

Answer 1

Let the total number of students in the class be $\mathrm{x}$

Percentage of girls in the class $=25\%$

Percentage of boys in the class $=100-25=75\%$

Now, according to the questions,

$$\begin{gathered} 75\%\mathrm{of}\mathrm{x}=30 \\ \Rightarrow \mathrm{x}\times 75\%=30 \\ \Rightarrow \mathrm{x}\times \frac{75}{100}=30 \end{gathered}$$

Transposing $\frac{75}{100}$ to RHS, we get,

$$\begin{gathered} \Rightarrow \mathrm{x}=\frac{30\times 100}{75} \\ \Rightarrow \mathrm{x}=\frac{3000}{75} \\ \Rightarrow \mathrm{x}=40 \end{gathered}$$

Hence, total number of students in the class is $40$.