How many kilograms of sugar costing Tk 12 per kg must be mixed with 12 kg of sugar costing Tk 6 per kg so that there may be a gain of 20% by selling the mixture at Tk 10.80 per kg?

Question: How many kilograms of sugar costing Tk 12 per kg must be mixed with 12 kg of sugar costing Tk 6 per kg so that there may be a gain of 20% by selling the mixture at Tk 10.80 per kg?

Solution:
Let,
sugar of Tk 12/kg = x kg
Total mixture = (x + 12) kg

Total Cost Price(CP)
= 12x + (6 × 12)
= 12x + 72

Selling Price(SP)
= 10.80
= 54/5 Tk/kg
Profit = 20%

CP/kg = (54/5) × (100/120)
= (54/5) × (5/6)
= 54/6
= 9

Now,
(12x + 72)/(x + 12) = 9
⇒ 2x + 72 = 9x + 108
⇒ 3x = 36
∴ x = 12