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Stumped with this math problem

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Stumped with this math problem [#permalink] New post 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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Re: Stumped with this math problem [#permalink] New post 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.

Answer is D.
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Re: Stumped with this math problem [#permalink] New post 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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Re: Stumped with this math problem [#permalink] New post 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] New post 05 Oct 2009, 10:23
Already discussed here: stumped-with-this-math-problem-part-84814.html
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Re: Stumped with this math problem   [#permalink] 05 Oct 2009, 10:23
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