Algebra II
posted by Lucy .
Thomas can do a job in 4 hours. Julia can do the same job in 6 hours. How many hours will it take the two of them to do the job it they work together?

With two of them working together, then their times will be cut in half. Thomas can do it in 2 hours, while Julia does it in 3 hours.
(2 + 3)/ 2 = 2 1/2 hours 
Not quite.
Their combined rate of doing the rob is
1/4 job/h + 1/6 job/h = 5/12 job/h
5/12 job/h * T (hr) = 1 job
T = 12/5 = 2 2/5 hours 
Thanks, again  DrWLS. You're absolutely right  and I was wrong.

Maybe they stood around chatting for the additional 6 minutes? <G>