GIVEN: Purchased milk from milkman = 16 L Mixed quantity of water = 4 L In process of making khoya, 50% of pure milk and 75% of water will vaporize. After making khoya it weights 1 L less than original weight. CALCULATION: Original weight of khoya = 50% of 16 + 25% of 4 = 8 + 1 = 9 L Let ‘x’ L water is mixed by milkman in the milk. So, Actual quantity of pure milk = (16 – x) Quantity of water = (4 + x) Actual quantity of khoya = 50% of (16 – x) + 25% of (4 + x) = 9 – 1 ⇒ 8 – 0.5x + 1 + 0.25x = 8 ⇒ 0.25x = 1 ⇒ x = 4 ∴ Required percentage = (4 / 16) × 100 = 25%