A man, a woman and a boy can do a piece of work in 6, 9 and 18 days respectively. How many boys must assist one man and one woman to do the work in 1 day ?

A. 5

B. 6

C. 9

D. 13

Answer: Option D

Solution(By Examveda Team)

(1 man + 1 woman)'s 1 day's work
$$\eqalign{ & = \frac{1}{6} + \frac{1}{9} \cr & = \frac{5}{{18}} \cr & {\text{Remaining work}} \cr & = \left( {1 - \frac{5}{{18}}} \right) \cr & = \frac{{13}}{{18}} \cr} $$
Work done by 1 boy in 1 day = $$\frac{1}{{18}}$$
$$\eqalign{ & \therefore {\text{Number of boys required}} \cr & = \left( {\frac{{13}}{{18}} \times 18} \right) \cr & = 13 \cr} $$