In what ratio should a vendor mix two types of pulses costing Rs. 16/Kg and Rs. 21/Kg respectively so as to get a mixture of Rs. 18/Kg?
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 = 21, A1 = 16, A = 18 we have n1 × (18 - 16) = n2 × (21 - 18), from where we get the required ratio as $n_1/n_2 = 3 : 2$.