A container holds 60 litres of milk. 12 litres are taken out and replaced with water. This is done once more. How much milk is now in the container?

💡 Solution & Explanation

Each time, 12 of the 60 litres is removed, so 48/60 of the milk stays. After the first time: 60 × 48/60 = 48 litres of milk. After the second time: 48 × 48/60 = 38.4 litres. Formula: milk left = V × (1 − x/V)ⁿ for n repetitions. Subtracting 12 twice (36 litres) is wrong because the second removal takes out some water too.