A milk man mixes 10% water in pure milk but he is not content with it so he again mixes 10% more water in the previous mixture .What is the profit percentage of milkman if he sells it at cost price?

Starting with 100 units milk: After 1st 10% water, milk=90, total=100. After 2nd 10% of mixture (10 units): milk=81, water=19, total=100. Finally milkman adds 10% of THIS mixture (10 units) containing 8.1 milk + 1.9 water: milk=89.1, water=20.1. Profit = (20.1/89.1)*100 = 22.56%, but this is cheating. Correct interpretation: 10% added twice to pure milk (not sequential): 100→110 (10 water)→121 (10+11 water). So 21 water in 121 total = 21/100 milk = 21% profit.