In what ratio should water (costing Rs. 0) be added to a liquid costing Rs. 12 per litre to make a profit of 25% when selling the diluted liquid at Rs. 13.75 per litre?

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?