A can do work alone in 15 days whereas B can destroy entire work in 20 days. They are working on alternate days with a working on the first day, B working on the second day, then how many days will work completed?

Answer 1

A does 4/60 and B undoes 3/60

so 1/60 completed every 2 days

after 112 days, 56/60 are done
... A completes the work on the 113th