How much chicory at Tk. 5 a kg should be added to 20 kg of coffee at Tk. 12 a kg so that the mixture be worth Tk. 7.50 a kg?

Question: How much chicory at Tk. 5 a kg should be added to 20 kg of coffee at Tk. 12 a kg so that the mixture be worth Tk. 7.50 a kg?

Solution:
Ratio in which coffee and chicory should be mixed
= 12 - 7.5 : 7.5 - 5 = 4.5 : 2.5 = 9 : 5.

Let x be quantity at Tk. 5 a kg
∴ 9 : 5 = x : 20
⇒ 5x = 180
⇒ x = 36