Both of the problems are very similar. I will solve one for you; you may want to try the second by yourself. If you still do not get it, I can help you again. The amount of alcohol in 250 solution = 45% Say, total quantity = X 45% of X = 112.50 mL But the solution has got only 50% of alcohol, so 2 * 112.50 = 225 The amount of wate = 250 - 225 = 25 mL