A and B can together finish a work 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?

Question: A and B can together finish a work 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?

Solution:
(A+B)'s 20 day's work
= (1/30)×20
= 2/3.
Remaining work = 1 - (2/3)
= 1/3

Now, 1/3 work is done by A in 20 days.
Whole work will be done by A in (20 × 3)
= 60 days.