In what ratio sugar at Rs 30/kg should be mixed with sugar at Rs 45/kg so that on selling mixture at Rs 42/kg there is a profit of 20%?

2 : 1

Selling price of the mixture = ₹42/kg with 20% profit.

So, the cost price of the mixture is:

$\text{CP} = \frac{42 \times 100}{120} = 35$

Now use the rule of alligation:

$\text{Ratio} = (45 - 35) : (35 - 30) = 10 : 5 = 2 : 1$

So, sugar costing ₹30/kg should be mixed with sugar costing ₹45/kg in the ratio: $2 : 1$