A fruit-seller buys mangoes at 6 for ₹50 and sells them at 5 for ₹60. His profit percent is:

Work with 30 mangoes, a number both counts divide: they cost $5\times 50$ = ₹250 and sell for $6\times 60$ = ₹360, a profit of ₹110 on ₹250 = 44%. Comparing ₹60 with ₹50 straight off gives 20% but ignores that one figure is for 5 mangoes and the other for 6; 110/360 = 30.6% works the profit out on the selling price; and rounding the cost off to ₹8 a mango against a ₹12 selling price suggests 50%.