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IR - speed

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metallicafan Master | Next Rank: 500 Posts Default Avatar
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IR - speed

Post Mon Jul 22, 2013 3:02 pm
A car is traveling on a straight stretch of roadway, and the speed of the car is increasing at a constant rate. At time 0 seconds, the speed of the car is V0 meters per second; 10 seconds later, the front bumper of the car has traveled 125 meters and the speed of the car is V10 meters per second.

In the table below, select values of V0 and V10 that are together consistent with the information provided. Make only two selections, one in each column.



My doubt is:
The question indicates that the speed of the car is increasing at a constant rate. So, is it talking about an arithmetic sequence, or a geometric sequence? According to the OE, the average speed is [m][fraction]1/2[/fraction]*( V0 + V10)[/m]. So, it seems that it is talking about an arithmetic sequence because that's the way we use to calculate the average in an arithmetic sequence. Please confirm.
However, I remember that, when a question mentions that something is increasing at a constant rate, we must multiply the first value by a constant, we shouldn't add. Please, your help.


OA:
V0 = 5 ; V10 = 20

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Post Mon Jul 22, 2013 8:13 pm
Hi metallicafan,

In these types of questions, a constant increase in speed would be considered an arithmetic sequence. If a question expected you to use a geometric sequence (which would be strange for an IR question), then the question would explain that idea in detail.

For this question though, you really wouldn't need much in the way of math skills. Since the car is traveling for 10 seconds but only travels 125 meters, it couldn't have been going too fast at the end (and as such, must have been going fairly slow in the beginning). The answer would have to be either 5|18 or 5|20 and with a little playing around, you'd prove which answer was correct.

GMAT assassins aren't born, they're made,
Rich

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