In a mixture of two oils A and B, the ratio of A to B is 3:2. If the cost of oil A is Rs. 60 per litre and that of oil B is Rs. 120 per litre, find the cost per litre of the resulting mixture.

The mixture costs Rs. 84 per litre.

Take 3 litres of A and 2 litres of B for the ratio 3:2.

Cost = 3 x 60 + 2 x 120 = 180 + 240 = Rs. 420.

Total volume = 3 + 2 = 5 litres.

Cost per litre = 420/5 = Rs. 84.