If you combine a certain amount of oil priced at Rs.40 per liter with 240 liters of another oil costing Rs.60 per liter, how many liters of the first oil must be added to obtain a blend priced at Rs.52 per liter?

Explanation

To find the quantity of oil at Rs.40 per liter to mix with 240 liters at Rs.60 per liter for a final price of Rs.52 per liter, use the weighted average formula. Let x be the liters of Rs.40 oil. Then, (40x + 60*240) / (x + 240) = 52. Solving for x gives 160 liters.