In a 90 litres mixture of milk and water, percentage of water is only 30%. The milkman gave 18 litres of this mixture to a customer and then added 18 litres of water to the remaining mixture. What is the percentage of milk in the final mixture ?

In 90 liters of mixture,
Amount of water=$$\frac{90\times30}{100}$$.
=27 liters.
Amount of milk=$$\frac{90\times70}{100}$$.
=63 liters.
Similarly, in 18 liters of mixture,
Amount of water=$$\frac{18\times30}{100}$$.
=5.4 liters.
Amount of milk=$$\frac{18\times70}{100}$$.
=12.6 liters.
After removing 18 liters of solution,
Amount of water=27-5.4=21.6 liters.
Amount of milk=63-12.6=50.4 liters.
After adding 18 liters of water,
Amount of water in the solution=21.6+18=39.6 liters.
Hence, Percentage of milk in solution=$$\frac{50.4}{50.4+39.6}\times 100$$.
=56%.
Hence, Option E is correct.