Two identical containers P and Q contain a mixture of milk and water in the ratio 1 : 1 and 3 : 1 respectively. In what ratio should the mixture be taken out from P and Q so that the milk to water ratio becomes 5 : 4?

The mixture is taken from P and Q in the ratio 7 : 2.

P has milk 1/2, Q has milk 3/4; target milk : water = 5 : 4.

Take p from P and q from Q; milk = p/2 + 3q/4, water = p/2 + q/4.

(p/2 + 3q/4) / (p/2 + q/4) = 5/4 gives 2p + 3q = 2.5p + 1.25q.

1.75q = 0.5p, so p : q = 7 : 2.