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?
40
50
54
60
Explanation:
A and B together complete the work in 30 days.
So, work done by A and B together in 1 day = 1/30
=> Work done by A and B together in 20 days = 20/30 = 2/3
So work remaining after 20 days when B leaves = 1 - 2/3 = 1/3
Given that A completes the remaining work in 20 days
=> A completes 1/3 work in 20 days
=> A completes the work in 20 $\times$ 3 = 60 days.