SOLUTION: Trimming hedges. Lourdes can trim the hedges around her property in 8 hours by using an electric hedge trimmer. Rafael can do the same job in 15 hours by using a manual trimmer.

Question 184018: Trimming hedges.
Lourdes can trim the hedges around her property in 8 hours by using an electric hedge trimmer. Rafael can do the same job in 15 hours by using a manual trimmer. How long would it take them to trim the hedges working together?
Found 2 solutions by stanbon, josmiceli:
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
Lourdes can trim the hedges around her property in 8 hours by using an electric hedge trimmer. Rafael can do the same job in 15 hours by using a manual trimmer. How long would it take them to trim the hedges working together?
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Lourdes DATA:
time = 8 hr/job ; rate = 1/8 job/hr.
---------------------------------------
Rafael DATA:
time = 15 hr/job ; rate = 1/15 job/hr.
---------------------------------------
Together DATA:
time = x hr/job ; rate = 1/x job/hr
=======================================
Equation:
rate + rate = together rate
1/8 + 1/15 = 1/x
Multiply thru by 120x to get:
15x + 8x= 120
23x = 120
x = 5.21 hrs (time to trim the hedges together)
====================================================
Cheers,
Stan H.

Answer by josmiceli(19441) (Show Source): You can put this solution on YOUR website!
To get the rate of hedge clipping with them working
together, I add the rates of them each working alone
In words:
(1 trimming job)/(Lourde's time) + (1 trimming job)/(Rafael's time) =
(1 trimming job)/(time working together)
given:
Lourde's time is hrs
Rafael's time is hrs
----------------------------

Multiply both sides by

Multiply both sides by

hrs

Working together, they finish in about 5 hrs and 13 min
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