9 liters of Petrol costing Rs. 21/liter is mixed with 15 liters of Kerosene costing Rs. 13/liter. What is the price of the mixture per liter?
Rs. 16 per liter.
Rs. 17 per liter.
Rs. 15 per liter.
Rs. 19 per liter.
We shall use the alligation formula. If a sample n1 has an average price of A1, and another sample n2 has an average price of A2, then the price of the mixture, A, is determined by the alligation formula as: n1(A - A1) = n2(A2 - A). Putting A2 = 13, A1 = 21, n1 = 9, n2 = 15, we have 9 × (A - 21) = 15 × (13 - A), from where we get A = Rs. 16 per liter.