posted by Karen .
If Sam can do a job in 4 days that Lisa can do in 6 days and Tom can do in 2 days, how long would the job take if they worked together to complete it?
combined rate = 1/4 + 1/6 + 1/2 = 11/12
so time taken for working at combined rate = 1/(11/12)
= 12/11 hours
or 1 hour and about 5 minutes