Concept: The question tests on Alligation
Solution:
Let the volumes be V1 and V2.
Concentration of Milk in V1 = 4/7∗100=400/7 %
Concentration of Milk in V2 = 2/5∗100=40%
Concentration of Milk in the final mixture = 1/2∗100=50%
Refer to the diagram below
We have V1/10=V2/(50/7)
Therefore V1/V2
=10/(50/7)
=70/50
=7/5 (option b)
