A milkman has 3 liters of 2% curd, and 2 liters of 12% curd. If he mixes equal quantities of the two curd samples, then what is the percentage curd in the mixture?
We shall use the alligation formula. If a sample n1 has an average property of A1, and another sample n2 has an average property of A2, then the average property of the mixture, A, is determined by the alligation formula as: n1(A - A1) = n2(A2 - A). Putting A2 = 12, A1 = 2, n1 = 3, n2 = 2, we have 3 × (A - 2) = 2 × (12 - A), from where we get A = 6%. The "property" in the alligation formula could be percentage, speed, weight, price, etc.,