A can do a piece of work in 6 days B in 9 days and C in 12 days. A and B starts the work together but after 2 days B had left and C joint with A till the completion of the work. How long did the work last?
They all in 2 days do=2x(1/6+1/9+1/12) part=13/18 part. B leaves.
Part of work left=1-13/18 part=5/18 part
C and A in 1 day do=(1/6+1/12) part=1/4 part
They can do 5/18 of the work in (5/18)x4 days=10/9 days
The work last for = 2+10/9 days=3 and 1/2 days