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# Stumped with this math problem

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Manager
Joined: 28 Mar 2009
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Stumped with this math problem [#permalink]

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04 Oct 2009, 22:04
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Hello, if anyone could help me figure out this problem I would very much appreciate it.

I treated it as a weighted average problem and got an answer of 37.5 which I rounded to 38, but that was clearly the wrong approach seeing as how the answer is 36.

Thanks
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Kudos [?]: 5 [0], given: 8

Manager
Joined: 25 Aug 2009
Posts: 165

Kudos [?]: 201 [0], given: 3

Location: Streamwood IL
Schools: Kellogg(Evening),Booth (Evening)
WE 1: 5 Years
Re: Stumped with this math problem [#permalink]

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05 Oct 2009, 09:08
Fuel used in the City trip = A =10/25 gal
Fuel used in the Highway trip = B = 50/40 gal
Total distance traveled = C = 60 miles
Total gasoline used = A+B = 33/20
Avg mpg = C/ (A+B) = 60*20/33 = 36.36 = 36 rounded off.

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Kudos [?]: 201 [0], given: 3

Manager
Joined: 25 Aug 2009
Posts: 165

Kudos [?]: 201 [0], given: 3

Location: Streamwood IL
Schools: Kellogg(Evening),Booth (Evening)
WE 1: 5 Years
Re: Stumped with this math problem [#permalink]

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05 Oct 2009, 09:12
Blayze as a rule of thumb, when you calculate averages never work with composites such as speed, momentum, density etc, always work with the basics such as distance, time, mass, volume and so on. Hope this helps resolve the mistake you made.
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Manager
Joined: 28 Mar 2009
Posts: 88

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Re: Stumped with this math problem [#permalink]

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05 Oct 2009, 09:51
Thanks Atish... that is so confusing lol

I was under the impression I was working off of distance because I was using distance to calculate the weights

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Re: Stumped with this math problem [#permalink]

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05 Oct 2009, 10:23
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Re: Stumped with this math problem   [#permalink] 05 Oct 2009, 10:23
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# Stumped with this math problem

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