There are two varieties of milk costing ₹70/litre and ₹50/litre respectively. If both varieties are mixed together, the price of the new mixture becomes ₹55/litre. Find the ratio in which the two types of milk were mixed.

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?