Pure milk costs Rs. 16 per litre. After adding water, a milkman sells the mixture at Rs. 15 per litre and thereby makes a profit of 25%. In what ratio does he mix milk with water?

A vessel has 20 litres of milk. From this vessel, 5 litres of milk is taken out and replaced by water. The process is repeated once more. Find the quantity of milk (in litres) remaining in the vessel.

A shopkeeper mixes 40 kg of rice costing ₹30/kg with 60 kg of rice costing ₹50/kg. What is the average price (in ₹/kg) of the mixture?