A milkman buys milk at Rs 25 per litre and adds 1/4 of water to it and sells the mixture at Rs 26 per litre. His gain (in %) is?

Step 1: Understand the composition of the mixture

• The milkman buys milk at Rs. 25 per litre.
• He adds 1/4 part water to the milk, which is free.
• This means for every 4 litres of milk, he adds 1 litre of water.
• Total quantity of the mixture becomes 4 + 1 = 5 litres.

Step 2: Calculate the cost price of the total mixture

Since he adds 1 litre of free water to 4 litres of milk,
Cost of 4 litres of milk = 4 × Rs. 25 = Rs. 100
Cost of 1 litre of water = Rs. 0 (it's free)
So, Total cost price = Rs. 100 for 5 litres

Step 3: Calculate the selling price of the mixture

He sells the entire 5 litres at Rs. 26 per litre:
Selling price = 5 × Rs. 26 = Rs. 130

Step 4: Calculate the profit made

Profit = Selling Price - Cost Price = Rs. 130 - Rs. 100 = Rs. 30

Step 5: Calculate the profit percentage

Profit % = (Profit / Cost Price) × 100
         = (30 / 100) × 100
         = 30%

Answer: 30%

By adding 1/4 part water to milk and selling the mixture at Rs. 26 per litre, the milkman earns a profit of 30% without increasing his cost.

This question is a great example of profit through adulteration. It shows how merchants can increase profit margins by mixing free substances like water and selling the mixture at the original price. This kind of problem is often featured in competitive exams like SSC, Banking, CAT, and state-level aptitude tests. Understanding this concept helps you spot hidden cost-saving techniques and profit strategies in real-life business transactions.