Question

A vessel contains a mixture of milk and water in the ratio of 9 : 5. How much quantity of the mixture must be drawn off and replaced with water, so that the ratio of milk and water becomes 5 : 7?

Answer 1

Final fraction of milk = initial fraction of milk * (1 – fraction of mixture taken out)n

Where ‘n’ is the number of times process is done

Thus, 1/2 = 5/8 * ( 1 – f )1

i.e. 1 – f = 4/5

i.e. f = 1/5