MY Solution that is very easy to understand: Let he has to take X ml of alcoholic solution and Y ml of water. now we need two equations involving X and Y to solve it. First equation: The final volume should be 250ml. Hence X + Y = 250 Second equation: The percentage of alcohol in the final solution should be 45. Hence: Volume of Alcohol / Total volume of solution = 0.45 (X/2) / ( X +Y) = 0.45 ( because, when we take total X alcoholic water, it will have only X/2 alcohol in it). Solving these two equations you get X = 225 ml and Y = 25 ml Cheers.