80 litres of water is mixed with a certain quantity of milk so that the mixture costs Rs 40 per litre. If the cost of pure milk is Rs 60 per litre and water is available free of cost, then the quantity of milk in the mixture is:

A shopkeeper mixes two types of rice in the ratio 5 : 3, where one type costs ₹75 per kg and the other costs ₹85 per kg. Find the average price per kg of the mixture.

In what ratio (cheaper to dearer) should a grocer mix two varieties of pulses costing ₹18 and ₹22 per kg, respectively, to obtain a mixture worth ₹19.50 per kg?