Correct Answer - Option 3 : 21 days
GIVEN:
Man's efficiency = 3 × women's efficiency
Boy's efficiency = 2 × women's efficiency
(3 women + 4 boys + 1 man)'s time = 3 days
FORMULA USED:
Work = Efficiency × time
CALCULATION:
Let the efficiency of a woman be 1 unit/day.
∴ Man's efficiency = 3 unit/day
Boy's efficiency = 2 unit/day
A.T.Q
Total work = (1 × 3 + 4 × 2 + 1 × 3) × 3 = 42 unit
Boy's time = 42/2 = 21 days
∴ A boy will take 21 days.