A and B can do a job in 10 days and 5 days, respectively. They worked together for two days, after which B was replaced by C and the work was finished in the next three days, How long will C alone take to finish 60% of the job?
Show answer & explanation
Correct answer: C
Explanation
The correct answer is option 3 i.e. 18 days
A can do a job in 10 days.
B can do a job in 5 days.
Efficiency = Total work/Time taken
Total work = LCM of 10 and 5 = 10
The efficiency of A = 10/10 = 1 unit/day
The efficiency of B = 10/5 = 2 units/day
A and B work for 2 days = (1 + 2) × 2 units = 6 units
Remaining work = (10 - 6) units = 4 units
A and C can complete the remaining work in 3 days.
A and C one-day work = 4/3
C one day work = (4/3) - 1 = 1/3
C can complete 60% of work in = 6/(1/3) = 18 days