A man pays Rs. 6.40 per litre of milk. He adds water and sells the mixture at Rs. 8 per litre, thereby making 37.5% profit. The proportion of water to milk received by the customers is

Customer ratio of Milk and Water is given by

Milk          ::        Water

  6.4                         0

          $\frac{8}{1 + \frac{3}{8}} =\frac{64}{11}$

  $\frac{64}{11}$                       $\frac{64}{10} - \frac{64}{11}$

=> Milk : Water = 110 : 11 = 10 : 1

Therefore, the proportionate of Water to Milk for Customer is 1 : 10