A milkman makes 20% profit by selling milk mixed with water at Rs. 9 per litre, if the cost price of 1 litre pure milk is Rs. 10, then the ratio of milk and water in the said mixture is = ?

Solution (By Examveda Team)

According to question,
S.P. at 20% profit = Rs. 9/litres
Cost of mixture $$ = \frac{9}{{120}} \times 100 = {\text{Rs}}{\text{.}}\,7.5/{\text{litre}}$$
Now, let the ratio of milk and water in the mixture = x : y
$$\eqalign{ & \Rightarrow \frac{{\left( {10 \times x} \right) + \left( {0 \times y} \right)}}{{x + y}} = 7.5 \cr & \Rightarrow 10x = 7.5\left( {x + y} \right) \cr & \Rightarrow x:y = 3:1 \cr} $$