SOLUTION: Rob takes 9 hours to clean the attic. Huong can clean the same attic in 15 hours. How long would it take if they worked together?

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Question 1012188: Rob takes 9 hours to clean the attic.
Huong can clean the same attic in 15 hours.
How long would it take if they worked together?
Found 2 solutions by ikleyn, josmiceli:
Answer by ikleyn(52794)   (Show Source): You can put this solution on YOUR website!
.
Rob takes 9 hours to clean the attic.
Huong can clean the same attic in 15 hours.
How long would it take if they worked together?
------------------------------------------------ 
Rob makes    of the job in one hour.
Huong makes  of the job in one hour.
Working together, they make  =  =  of the job in one hour.
Hence, it will take  =  hours for Rob and Huong to make the job working together.

See the lesson Using fractions to solve word problems on joint work in this site for more solved problems on joint work.


Answer by josmiceli(19441)   (Show Source): You can put this solution on YOUR website!
Add their rates of working to get their
rate of working together
Rob's rate:
[ 1 attic cleaned ] / [ 9 hrs ]
Huong's rate:
[ 1 attic cleaned ] / [ 15 hrs ]
--------------------------
Let their rate working together =
[ 1 attic cleaned ] / [ t hrs ]

Multiply both sides by



and

Working together, it will take them
5 hrs 37 min 30 sec
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