A can do a piece of work in 42 days and B is thrice as efficient as A. If B joins A on 22nd day then in how many days will the work be completed?

Where, W = The work, E = The efficiency, and T = The time

Let us assume the work will be completed in X days
⇒ The one day work of A = 1/42
⇒ The one day work of B = 3 × (1/42) = 1/14
⇒ The 21 days work of A = 21 × (1/42) = 1/2
⇒ The remaining work = 1 - 1/2 = 1/2
⇒ The efficiency of A and B together = (1/42 + 1/14) = 4/42 = 2/21
⇒ The remaining work will be completed = (1/2) × (21/2) = 21/4 = 5.25 days

∴ The required result will be 5.25 days.