Let the milk he bought is 1000 ml Let C.P of 1000 ml is Rs. 100 Here let he is mixing K ml of water He is getting 30% profit => Now, the selling price is also Rs. 100 for 1000 ml => 100 : K% = 100 : 30 10 : 3 is ratio of milk to water => Percentage of milk = 10 x 100/13 = 1000/13 = 76.92%