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Posted by **Heather** on Wednesday, April 24, 2013 at 5:34pm.

14.It takes 9 hours for Isabella to rake leaves by herself,but her brother Matthew can work three times as fast.If they work together, how long will it take them to rake leaves?

Rate Time Work Done

Isabella

Matthew

- algebra -
**Melannie**, Wednesday, April 24, 2013 at 6:10pmI think the answer is 3 hours

- algebra -
**Reiny**, Wednesday, April 24, 2013 at 6:26pmIsabelle's rate = lawn/9

(Matt could do it in 3 hours)

Matt's rate = lawn/3

combined rate = lawn/9 + lawn/3 = 4lawn/9

time at combined rate = lawn/(4lawn/9))

= 9/4 hrs or 2.25 hrs or 2 hours and 15 minutes

( since "lawn" canceled, we could have just used

1/9 + 1/3 = 4/9

then time = 1/(4/9) = 9/4 = 2.25 )

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