A person sold 25 articles for Rs. 2,500 and incurred a loss of 10%. How many articles should he sell for Rs. 2,400 to make a profit of 20%?

Answer: Option D

A person sold 25 article Rs. 2500
Selling price of 1 article $$=\frac{2500}{25}=100$$
Cost price of 1 article $$=100\times \frac{100}{90}=\frac{1000}{9}$$
New selling price of 1 article = $$=\frac{1000}{9}\times \frac{120}{100}=\frac{400}{3}$$
Number of articles sold in Rs. 2400 $$=2400÷\frac{400}{3}=18$$