Five litres of water is added to a certain quantity of pure milk costing Rs. 60 per litre. If by selling the mixture at the same price as before, a profit of 20% is made, then the amount of pure milk in the mixture is :
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 25 litres
Let the quantity of pure milk be x litres. Water is free, so the cost is only the milk:
\(\text{CP} = 60x\)
The whole mixture of (x + 5) litres is sold at Rs. 60 a litre:
\(\text{SP} = 60(x + 5)\)
A 20% profit means SP = 1.2 × CP:
\(60(x + 5) = 1.2 \times 60x\)
\(x + 5 = 1.2x\)
\(0.2x = 5\)
\(x = 25\)
So the mixture contains 25 litres of pure milk.
Why the other options are incorrect
Option (1) 20 litres — Incorrect. Cost 20 × 60 = 1200, selling 25 litres gives 1500, a profit of 25%, not 20%.
Option (3) 30 litres — Incorrect. 30 litres is the whole mixture (25 litres of milk + 5 litres of water), not the pure milk.
Option (4) 40 litres — Incorrect. Cost 40 × 60 = 2400, selling 45 litres gives 2700, a profit of 12.5%, not 20%.