Two varieties of dal cost ₹90 per kg and ₹120 per kg. In what ratio (cheaper : costlier) should they be mixed so that the mixture costs ₹100 per kg?

Explanation

1. 01

   The cheaper dal is $100 - 90 = 10$ below the target; the costlier one is $120 - 100 = 20$ above it.

2. 02

   Cheaper : costlier = $20 : 10 = 2 : 1$ (distances taken crosswise).

3. 03

   Check: $\frac{2 \times 90 + 1 \times 120}{3} = \frac{300}{3} = 100$.