The ratio of milk and water in 40 litres of mixture is 3:1. How much water must be added to make the ratio 2:1?

प्रारंभ में: दूध=30L, पानी=10L। माना मिलाया गया पानी x है। 30 / (10+x) = 2/1, 30 = 20 + 2x, 2x = 10, x = 5L।