Sugar costing Rs.14 per kg and Rs.17 per kg is mixed and the mixture is sold at Rs.18 per kg to earn a profit of 20%. In what ratio should the cheaper sugar be mixed with the dearer sugar?

If the selling price is Rs.18 with a profit of 20%, then the cost price of the mixture is $18/1.2=15$ rupees per kg. Now apply alligation: $\frac{\text{cheaper}}{\text{dearer}}=\frac{17-15}{15-14}=\frac{2}{1}$. Hence the required ratio is $2:1$.