A trader has 60 kg of grain. He sells part of it at 10% profit and the rest at 25% profit, and gains 15% on the whole. How much did he sell at 10% profit?

Explanation

1. 01

   Alligation on the profit rates: $(25 - 15) : (15 - 10) = 10 : 5 = 2 : 1$.

2. 02

   So $\frac{2}{3} \times 60 = 40$ kg was sold at 10%.