A is thrice as productive as C. Together they can complete a job in 22.5 days. If B joins them after they have worked for 15 days, then in how many days can they finish the rest of the job, while B alone can do the job in 15 days?
A is thrice as productive as C. Together they can complete a job in 22.5 days. If B joins them after they have worked for 15 days, then in how many days can they finish the rest of the job, while B alone can do the job in 15 days? Correct Answer 3
Shortcut Trick
Work = Efficiency × Time
According to the question
Efficiency of A = 3
Efficiency of C = 1
Let the total work be 4 × 22.5 = 90
So, the Efficiency of B = 90 ÷ 15 = 6 unit per day
Accroding to the question
15 days work of (A + C) = 15 × 4 = 60
Rest work = (90 - 60) units = 30 units
Now, Combined efficiency of A + B + C = 10
Time to complete the remaining work = 30 ÷ 10 = 3 days
∴ The required time is 3 days.
Remaining job is (1 - 2/3) = 1/3 part
B alone can do the job in 15 days
⇒ In 1 day B can do 1/15 part of the job
Together in 1 day A, B and C can do (1/22.5 + 1/15) part of the job
⇒ (2 + 3)/45
⇒ 5/45
⇒ 1/9 part of the job
⇒ Together A, B and C can complete the job in 9 days
To complete the remaining 1/3 part of the job they together will take time (9/3) = 3 days.
∴ in 3 days they will complete the rest of the job.