# math

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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 -

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 -

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

• math -

7/12

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