UPSC Prelims 2026 CSAT, question 22

Topic: Arithmetic

Q22

What is the minimum number of times one needs to measure to get 298 litres of water from a tank, if the measuring cylinders have capacities 1 litre, 6 litres, 25 litres and 100 litres?

(a) 4
(b) 5Correct answer
(c) 9
(d) 13

Solution.

Answer: (b) 5

Using the $100$ -litre cylinder $3$ times measures $300$ litres, and removing $1$ litre twice using the $1$ -litre cylinder leaves $300 - 2 = 298$ litres in $3 + 2 = 5$ measurements.
Four measurements cannot reach $298$ litres because $300 - 298 = 2$ is not a single cylinder capacity.

Trap: If water cannot be poured back, the fewest measurements are $2 \times 100 + 2 \times 25 + 8 \times 6 = 298$ , which is 12 and not an option.