MAT Exam 2020 Paper

Concept:With a fixed amount spent, a fall in price increases the number of gallons bought. Compare the quantities before and after the reduction.Explanation:Let the total amount spent be ₹1800 and the original price be $P$ rupees per gallon.After a $10\%$ reduction, the new price becomes$$\frac{90}{100}P = \frac{9P}{10}.$$Original gallons bought: $\frac{1800}{P}$.Gallons bought after reduction: $\frac{1800}{9P/10} = \frac{2000}{P}$.The increase is 5 gallons, so$$\frac{2000}{P} - \frac{1800}{P} = 5.$$$$\Rightarrow \frac{200}{P} = 5.$$$$\Rightarrow P = 40.$$Thus, the original price is ₹40 per gallon.Answer:Original price of petrol = ₹40 per gallon.Hence, the correct option is C.