In what ratio must pulses at ₹72 per kg be mixed with pulses ₹90 per kg so that the mixture be worth ₹80 per kg?

5 : 4

The correct answer is Option (2) → 5 : 4 **

Let the ratio of quantities be $x : y$.

Prices:

Cheaper = ₹72

Costlier = ₹90

Mean price = ₹80

Alligation differences:

$90 - 80 = 10$

$80 - 72 = 8$

Ratio is taken opposite to the differences:

Cheaper : Costlier = $10 : 8 = 5 : 4$

The pulses must be mixed in the ratio $5 : 4$.