A and B can together finish work in 30 days. They worked together for 20 days and then B left. After another 20 days, A finished the remaining work. In how many days, A alone can finish the work?
(A + B)'s 20 day's work = `(1/30xx20)=2/3`
Remaining work = `(1-2/3)=1/3`
Now, `1/3` work is done by A in 20 days.
Therefore, the whole work will be done by A in (20 x 3) = 60 days