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### Question

Two types of petrols having the prices per liter as Rs. 13 and Rs. 5 are mixed in the ratio 2 : 14. What is the price of the mixture per liter?

**A**

Rs. 6 per liter.

**B**

Rs. 7 per liter.

**C**

Rs. 5 per liter.

**D**

Rs. 9 per liter.

**Soln.**

**Ans: a**

If a sample n_{1} has an average price of A_{1}, and another sample n_{2} has an average price of A_{2}, then the price of the mixture, A, is determined by the alligation formula as: n_{1}(A - A_{1}) = n_{2}(A_{2} - A). Putting A_{2} = 5, A_{1} = 13, n1 = 2, n2 = 14, we have 2 × (A - 13) = 14 × (5 - A), from where we get A = Rs. 6 per liter.