Posted by **Kacey** on Friday, May 1, 2009 at 2:05am.

A can paint a room in 3 hours, and B can paint a room in 4 hours. How long will it take if they paint it together?

- math -
**RickP**, Friday, May 1, 2009 at 3:10am
Use the equation

Tt = 1/Tf + 1/Ts

where Tt is the total time, Tf is the first person's time, and Ts is the second person's time. Now just plug and chug.

- math -
**Damon**, Friday, May 1, 2009 at 6:36am
ah:

{ 1/Tt } = 1/Tf + 1/Ts

because

A --> 1/3 rooms per hr

B --> 1/4 rooms/hr

(A+B) --> 1/3 + 1/4 rooms/hr = 7/12 rooms per hr

which is 12/7 hours/room

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