Question

A can complete the work in 12day while B can complete it in 15day.they start the work
together but A left after 4days. In how many days the work will be completed?

Answer 1

work of A in 1 day = 1/12

work of B in 1 day = 1/15

they start working together but A left after 4 days =

1/12 + 1/15 = (5 +4)/60 = 9/60*4 = 9/15

Total work - work done = 1 - 9/15 = 6/15= 2/5

so days take to complete the work = 5/2days