A vessel full of water weighs 40 kg. If it is one-third filled, its weight becomes 20 kg. What is the weight of the empty vessel?
Answer & explanation
Answer: (a) 10 kg
Going from full to one-third full removes two-thirds of the water and 20 kg of weight, so the full water weighs 30 kg. The empty vessel is 40 − 30 = 10 kg.
- Full: vessel + water = 40 kg. One-third full: vessel + water/3 = 20 kg.
- Subtracting: (2/3) × water = 20 kg, so water = 30 kg.
- Empty vessel = 40 − 30 = 10 kg.
- Check: 10 + 30/3 = 20 kg.
Remember · Subtract the two readings: the difference belongs to the water alone, which fixes the water's full weight.
Question and answer: UPSC's official GS Paper II (2020, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). ·