Two containers of the same volume are 40% and 50% full of water, respectively. They are then filled completely with milk. If the contents of both containers are mixed in a larger vessel, what is the percentage of milk in the final mixture?

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?