math
posted by tammy .
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 Sam, Lisa, and Tom worked together to complete it?
A. 0.8 days
B. 1.09 days
C. 1.23 days
D. 1.65 days
E. 1.97 days
thanks.

First add the "jobs per day" rates of all three people.
1/4 + 1/6 + 1/2 = (3 + 2 + 6)/12 = 11/12 jobs per day
Then divide 1 job by 11/12 jobs/day to get the answer: 12/11 = 1.09 days