A and B can do a work in 6 days. B alone can do in 16 days. After 3 days B withdraws. Then how many days can be needed by A to do the work alone?

Answer 1

-- B can do the job alone in 16 days.

-- So B does 1/16 of the job per day.

-- In 6 days, B does 6/16 = 3/8 of the job.

-- If A and B working together do the job in 6 days, then A does the other 5/8 of the job in 6 days.

-- So A does 5/48 of the job each day.

-- If they begin together, then after 3 days, A has done 5/16 and B has done 3/16.

Together, they've finished 8/16 = 1/2 of the job. Not so surprising, when we recall

that it takes them 6 days to do the whole thing together.

-- Half of the job then remains for A to finish on his own. Since he does 5/48 per day,

he needs 24/5 = 4.8 days to finish off the last half.

4.8 more days