The ratio of acid and water in solution A and solution B is 7 : 8 and 9 : 11, respectively. 3 litres of solution A is mixed with 4 litres of solution B, and 1 litre of water is also added to it. What is the percentage of acid in the resulting solution?

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?