Geometry and mensuration: previous-year questions
21 real UPSC Prelims questions (2011–2026) with the official answer and a clear explanation. 4 of them came in the last five papers.
How often UPSC asks this
Questions per year, counted from the official papers.
Attempt the questions
Newest papers first. Tap an option; the answer and the reason appear instantly.
A village having a population of 4000 requires 150 litres of water per head per day. It has a tank measuring 20 m × 15 m × 6 m. The water of this tank will last for
Answer (b) & explanation
3 days is correct (b). Step 1: the tank's volume = 20 × 15 × 6 = 1,800 m³. Since 1 m³ = 1,000 litres, it holds 18,00,000 litres. Step 2: the village needs 4,000 people × 150 litres = 6,00,000 litres every day. Step 3: the water lasts 18,00,000 ÷ 6,00,000 = 3 days. So (a), (c) and (d) fail.
Tip: always convert units before dividing. Remember that 1 cubic metre is 1,000 litres; forgetting this gives answers that are a thousand times too big or too small. Write the units next to each number as you go.
Answer as per the official UPSC answer key.