दूध के एक नमूने में 50% पानी है। यदि इस दूध का 1/3 भाग इतनी ही मात्रा के शुद्ध दूध में मिलाया जाए, तो नए मिश्रण में पानी की मात्रा कितने प्रतिशत तक कम हो जाएगी?
Read this question in English
There is a milk sample with 50% water in it. If 1/3rd of this milk is added to equal amount of pure milk, then water in the new mixture will fall down to
(a) 25% · (b) 30% · (c) 35% · (d) 40%
उत्तर और व्याख्या · explanation in English
Answer: (a) 25%
Take the one-third portion as 1 litre: it holds 0.5 litre of water. Adding 1 litre of pure milk makes 2 litres with the same 0.5 litre of water, which is 25%.
- Let the portion taken (1/3rd of the sample) be 1 litre; at 50% water it has 0.5 litre of water.
- Add an equal amount (1 litre) of pure milk, which has no water: total 2 litres.
- Water = 0.5 ÷ 2 = 25%.
Remember · Adding an equal amount of the pure component halves the concentration; the size of the portion taken does not matter.
Question and answer: UPSC's official GS Paper II (2017, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). ·