A milkman professes to sell his milk at cost price but he mixes it with water and thereby gains 40%. Find the percentage of water in the mixture (rounded to one decimal place). 

Given:

A dishonest milkman professes to sell his milk at cost price, but he mixes it with water and gains 40%

Formula used:

Profit = SP - CP

Calculations:

Let milk bought (cost price) be 1 litres at Rs. 100 and profit = 40

∴ Selling price = 100 + 40 = Rs. 140

As the selling price of 1 litre was Rs. 100(same as cost)

Quantity sold = \(\dfrac{140}{100}\) = 1.4 litre

Hence, water added = 1.4 - 1 = 0.4 litres

Percentage of water = \(\dfrac{0.4}{1.40}\) × 100 = 28.6%

∴ The correct answer is Option (1).