Mary paid 15% of her monthly salary towards an EMI. From the remaining salary. she paid 10% as Internet bill and 20% as rent. If after the mentioned expenses she was left with Rs. 24,990 /-, what was Mary's monthly salary ?

Let Mary's monthly salary = Rs. $$100x$$

Money spent on EMI = $$\frac{15}{100} \times 100x = 15x$$

Amount left = $$100x - 15x = 85x$$

% amount left after paying internet bill and rent = $$100 - (10 + 20) = 70 \%$$

=> Amount left = $$\frac{70}{100} \times 85x = 24,990$$

=> $$\frac{7 \times 17x}{2} = 24,990$$

=> $$x = \frac{24,990 \times 2}{7 \times 17}$$

=> $$x = 210 \times 2 = 420$$

$$\therefore$$ Mary's monthly salary = $$100 \times 42$$ = Rs. $$42,000$$