A producer of a tea blends two varieties of tea from tea gardens one costing ₹ 18 per kg and another ₹ 20 kg in the ratio 5 : 3. If he sells the blended variety at ₹ 21 per kg, then his gain percentage is

Let quantities of two types of tea costing ₹ 18 per kg and ₹ 20 per kg be 5W kg and 3W kg. respectively.
Then, CP of tea = (18 x 5W) + (20 x 3W)
= 90W + 60W = 150W
SP of tea = 21 x 8W = 168W
Profit percent = [(168W - 150W) / 150W] x 100%
= (18/150) x 100% = 12%