200 mL of a 30% NaOH solution is mixed with 300 mL of a 40% NaOH solution. Assuming the mass percentage varies directly with volume percentage, the concentration of the mixture in terms of mass % is:

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?