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math word problem

Susan can wax her car in 2 hr(s). When she works together with Helga, they can wax the car in 30 minute(s). How long would it take Helga, working by herself, to wax the car?

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Robert A. | Certified Teacher and Engineer - Tutoring Physics, Maths, and SciencesCertified Teacher and Engineer - Tutorin...
5.0 5.0 (114 lesson ratings) (114)
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If you add units to this equation it will make a lot more sense.
And the solution gives an answer of x=2/3, but 2/3's what?  day, hour, min
 
Susan is 1 car per 2 hours
Helga is 1 car per x.
Together 1 car per 2 hours + 1 car per x = 1 car per (1/2)hour
then 1 car / 2 hours + 1 car / x = 1 car / (1/2) hour = 2 cars / hour
       1 car / x = 2 cars / hour - 1 car / 2 hours
                     = 4 cars / 2 hour - 1 car / 2 hours    
                    = 3 cars / 2 hour
So  1 car / x = 3/2 cars/hour
Therefor  x = 2/3 hours / car
Deanna L. | Electrical engineering major and music lover with MIT degreeElectrical engineering major and music l...
4.9 4.9 (127 lesson ratings) (127)
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To set up this equation, Susan is 1/2 and Helga is 1/x. Together 1/2 + 1/x = 1/(1/2) = 2. Then 1/x=3/2 and x= 2/3. Hope that helps!
 
Deanna