A man earns ₹ 25,440 per month. He spends $\dfrac{1}{4}$ of it on house rent, $\dfrac{3}{8}$ on food and clothes, $\dfrac{1}{10}$ on insurance and $\dfrac{1}{5}$ on other items. The rest he saves. How much does he save each month?

Given,

Total salary = ₹ 25440

House rent = ​$\dfrac{1}{4}$ part of the salary

Food & clothes = ​$\dfrac{3}{8}$ part of the salary

Insurance = $\dfrac{1}{10}$ part of the salary

Other items = $\dfrac{1}{5}$​ part of the salary

$\text{Total fraction spent } = \dfrac{1}{4} + \dfrac{3}{8} + \dfrac{1}{10} + \dfrac{1}{5}\\[1em] = \dfrac{1 \times 10}{4 \times 10} + \dfrac{3 \times 5}{8 \times 5} + \dfrac{1 \times 4}{10 \times 4} + \dfrac{1 \times 8}{5 \times 8}\\[1em] = \dfrac{10}{40} + \dfrac{15}{40} + \dfrac{4}{40} + \dfrac{8}{40}\\[1em] = \dfrac{10 + 15 + 4 + 8}{40}\\[1em] = \dfrac{37}{40}\\[1em]$

Saving fraction = 1 - Total spent fraction

$\Rightarrow \text{Saving fraction } = 1 - \dfrac{37}{40} \\[1em] = \dfrac{40}{40} - \dfrac{37}{40} \\[1em] = \dfrac{40 - 37}{40} \\[1em] = \dfrac{3}{40} \\[1em]$

Saving amount = Saving fraction × Salary

= $\dfrac{3}{40} \times 25,440 = \dfrac{3 \times 25,440}{40} = \dfrac{76,320}{40} = 1,908$.

Hence, saving per month = ₹ 1,908.