Given∶ Cost of 27 gm gold = Rs. 7 per gm S.P. of 1 gm of mixture = Rs. 9.24 per gm Gain = 10% Cost of gold that have to mixed = Rs. 9 per gm Formula Used∶ Basics of ratios, Rule of alligation, Calculation∶ S.P. of 1 g of mixture = Rs. 9.24, Gain = 10% CP of 1 g of mixture = (100/110) × 9.24 = Rs. 8.40 By the rule of alligation, Ratio of quantities of 1st and 2nd type = 14 ∶ 6 = 7 ∶ 3 Let x gm of gold of 1st type be mixed with 27 g of gold of 2nd type. According to question, 7 ∶ 3 = x ∶ 27 ⇒ x = (7 × 27)/3 = 63 ∴ 63 g of gold costing Rs.9 per gm must be mixed with 27 gof gold costing Rs. 7 per gm, so that the may be a gain of 10% by selling the mixture at Rs. 9.24 per gm.