A mixture of 30 liters contains milk and water in the ratio 7 : 3. How much water should be added so that the ratio becomes 3 : 7?

दूध = 21L, पानी = 9L। नए अनुपात 3:7 में, दूध (3 इकाई) = 21L => 1 इकाई = 7L। नया पानी (7 इकाई) = 49L। मिलाया गया पानी = 49 - 9 = 40L।