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# GMAT club Test m15#32

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GMAT club Test m15#32 [#permalink]  05 Oct 2010, 12:20
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Question Stats:

75% (02:51) correct 25% (02:28) wrong based on 0 sessions
If a car went the first third of the distance at 80 kmh, the second third at 24 kmh, and the last third at 48 kmh, what was the average speed of the car for the entire trip?

(C) 2008 GMAT Club - m15#32

* 36 kmh
* 40 kmh
* 42 kmh
* 44 kmh
* 50 kmh
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Re: GMAT club Test m15#32 [#permalink]  05 Oct 2010, 12:41
AndreG wrote:
If a car went the first third of the distance at 80 kmh, the second third at 24 kmh, and the last third at 48 kmh, what was the average speed of the car for the entire trip?

(C) 2008 GMAT Club - m15#32

* 36 kmh
* 40 kmh
* 42 kmh
* 44 kmh
* 50 kmh

Average \ speed=\frac{total \ distance}{total \ time}, let the total distance be 3x, then: total \ time=\frac{x}{80}+\frac{x}{24}+\frac{x}{48}=\frac{18x}{240};

Average \ speed=\frac{total \ distance}{total \ time}=\frac{3x}{\frac{18x}{240}}=\frac{240*3}{18}=40.

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Re: GMAT club Test m15#32 [#permalink]  05 Oct 2010, 12:44
Thanks! I confused distance with time and just couldnt wrap my head around where I went wrong
Re: GMAT club Test m15#32   [#permalink] 05 Oct 2010, 12:44
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