30 men and 20 women can complete a work in 50 days and 75 days, respectively. If the efficiency of a child is 60% that of a woman, then in how many days 40 children complete the work by working together.

Correct option is B

Let the efficiency of a man and a woman be m and w units/day respectively.
Given, 30m×50=20w×75

The efficiency of a child = a × (60/100) = 0.6a units/day
Required days =

= 62.5 days