In what ratio a shopkeeper must add milk and water so that on selling mixture at 15% more than cost price of milk he may get a profit of 25?

Let milk = m, water = w. Cost price of mixture = m (assuming milk cost = 1 per unit). Selling price = 1.15m (15% above milk's cost). Required profit = 25%, so effective cost must be: 1.15m / 1.25 = 0.92m. This means only 92% is milk, so 8% is water. Ratio milk:water = 92:8 = 23:2. The mixture is diluted enough that selling at just 15% premium still gives 25% profit.