Some apples are bought at 5 for ₹ 10 and sold at 6 for ₹ 15. What is the gain percent?

Let number of apples bought = 5 x 6 = 30 [LCM of 5 and 6]
CP = (10/5) x 30 = ₹ 60
SP = (15/6) x 30 = ₹ 75
∴ Gain = SP - CP = 75 - 60 = ₹ 15
∴ Gain % = (15/60) x 100 % = 25%