math
posted by dolores .
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 sam, lisa, and tom worked together to complete it?

Sam's rate = job/4
Lisa's rate = job/6
Tom's rate = job/2
time for all 3 working together
= job/(job/4 + job/6 + job/2)
= job/(11job/12)
= job * 12/(11job)
= 12/11
it would take them 1 1/11 days 
thanks but the answer is 13 i just don't know how to get it.

The answer of 13 days would be totally illogical!
Gee, Tom working alone can do the job in 2 days, and then he even has help, so it would obviously take less than 2 days !!!!