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# A certain car averages 25 miles per gallon of gasoline when

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Joined: 15 Jul 2005
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A certain car averages 25 miles per gallon of gasoline when [#permalink]  28 Aug 2005, 05:36
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A certain car averages 25 miles per gallon of gasoline when driven in the city and 40 miles per gallon when driven on the highway. According to these rates, which of the following is closest to the number of miles per gallon that the car averages when it is driven 10 miles in the city and 50 miles on the highway?

a) 28
b) 30
c) 33
d) 36
e) 38

This question I got right with a guess as I was running out of time. I feel like I understand how to do it but can't get the answer to correspond to the work that I do. The answer is 36. How do you get that number. I assumed here you multiply 25 by 10 and 50 by 40, add them, and divide by 60. However this comes out to 37.5. Any ideas?
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Joined: 29 Nov 2004
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Location: Chicago
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Re: PS - miles per gallon....from the PP....help! [#permalink]  28 Aug 2005, 05:45
[quote="mophead"]3) A certain car averages 25 miles per gallon of gasoline when driven in the city and 40 miles per gallon when driven on the highway. According to these rates, which of the following is closest to the number of miles per gallon that the car averages when it is driven 10 miles in the city and 50 miles on the highway?

a) 28
b) 30
c) 33
d) 36
e) 38

The correct approach is

10 miles in city, will take 10/25 = 2/5 gallon
50 miles in highway will take 50/40 = 5/4 gallon

so (2/5 + 5/4) gallon for (50 + 10) miles so for 1 gallon 60*20/3 = 36.37 ~ 36
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Fear Mediocrity, Respect Ignorance

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Joined: 07 Jul 2004
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In city: 25 miles/gallon
On highway: 40 miles/gallon

10 miles in city require = 10/25 = 2/5 = 0.4 gallons
50 miles on highway requires = 50/40 = 5/4 = 1.25 gallons

Total distance = 60 miles
Total gasoline used = 1.64 gallons

SO per miles/gallone = 60/1.64 = 6000/164 = 3000/82 = 1500/41 ~ = 1500/40 = 150/4 = 37 gallons...

I would pick D as we rounded down the denominator and the value should be less than 37.
Director
Joined: 11 Mar 2005
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I think best way is

1. calculate the gallons used
- 10/25 + 50/40 = 33/20 galleons
2. calculate the miles driven
= 60 miles

hence 60/ (33/20) = 1200/33 = 36.3
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