self doubts

Question

Two friends A and B were employed to do a work. Initial deadline was fixed at 24 days. Both started working together but after 20 days, A left the work and the whole work took 30 days to complete. In how much time can B alone can do the work?

( In this question what in initial unit to do work or total work)

Answer 1

At first 1/A + 1/B = 1/24

But A left after 20 days, so

20/A + 30/B  = 1

Solving these two equations will give B completes the work in 60 days alone.

Answer 2

so both A and B worked for 20 days so reaming work = 24-20 = 4 days
so B completed 4 days work in 10 days
therefore for completing 24 days work B will take 10*6 = 60 days