1 liter of drink contain water = 15% 12l of drink contain water = 15 % 12l of drink contain water at 15% = 1.8l 12l of drink contain water at 50% = 6l Water to add in 15% water drink = 6l – 1.8l = 4.2l After adding 4.2l of water in 12l 15% water drink, we get 50% water drink.