A and B can do a work in 12 days and 18 days, respectively. They worked for 4 days after which B was replaced by C and the remaining work was completed by A and C in the next 4 days. In how many days will C alone complete 50% of the same work?

A. 24

B. 18

C. 21

D. 36

Answer: Option B

Solution (By Examveda Team)

4 day work = 5 × 4 = 20
Remaining work = 36 - 20 = 16
(A + C) complete in 4 days
A + C $$ \to \frac{{16}}{4} = 4$$
3 + C = 4
C = 1
50% of work = $$\frac{{36}}{2}$$ = 18
C do = $$\frac{{18}}{1}$$ = 18 days