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Average Speed Concept

by asbestos » Sat Jun 20, 2009 1:59 am
At what speed was a car traveling when it had completed half of the distance of a trip?

(1) The car was traveling at an average speed of 65 miles per hour.

(2) The entire trip was 190 miles long and took 3 hours to complete.

A) Statement (1) BY ITSELF is sufficient to answer the question, but statement (2) by itself is not.

B) Statement (2) BY ITSELF is sufficient to answer the question, but statement (1) by itself is not.

C) Statements (1) and (2) TAKEN TOGETHER are sufficient to answer the question, even though NEITHER statement BY ITSELF is sufficient.

D) Either statement BY ITSELF is sufficient to answer the question.

E) Statements (1) and (2) TAKEN TOGETHER are NOT sufficient to answer the question, requiring more data pertaining to the problem.
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by ssmiles08 » Sat Jun 20, 2009 5:09 am
If I am reading this correctly, the question is asking for it's instantaneous velocity, which is impossible to find with the 2 choices provided below.

So I will go for (E)

OA?
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Re: Average Speed Concept

by Stuart@KaplanGMAT » Sat Jun 20, 2009 11:40 am
asbestos wrote:At what speed was a car traveling when it had completed half of the distance of a trip?

(1) The car was traveling at an average speed of 65 miles per hour.

(2) The entire trip was 190 miles long and took 3 hours to complete.
To be honest, I don't even understand the question. What's the source?

Here are some problems:

From the question, it sounds like we're asked for instantaneous speed at the halfway point, which is going to be impossible to calculate with GMAT level math. Short of applying physics, pretty much the only way to know the instantaneous speed is to.. umm.. know the instantaneous speed (we don't need to know kinematics for the GMAT).

Statement (1) makes no sense in a vacuum. "The car was traveling at an average speed of 65 miles per hour" when? For the entire trip? For the first half of the trip? A real GMAT question would be more specific. Without context, "was traveling" is the wrong verb tense for this question.

Statement (1), if it does refer to the entire trip, contradicts statement (2). Based on (2), the average speed for the entire trip is 190/3 which does NOT equal 65. On the GMAT, the statements will NEVER contradict each other.

So, either the poster didn't properly post the question (always a possibility) or it's a horribly written question (also a possibility) or both (often the case).
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Re: Average Speed Concept

by bluementor » Sat Jun 20, 2009 11:55 am
Stuart Kovinsky wrote:
asbestos wrote:At what speed was a car traveling when it had completed half of the distance of a trip?

(1) The car was traveling at an average speed of 65 miles per hour.

(2) The entire trip was 190 miles long and took 3 hours to complete.
To be honest, I don't even understand the question. What's the source?
This question is very similar to OG12 DS Q104 (pg 282). OA is E.

-BM-
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Re: Average Speed Concept

by Stuart@KaplanGMAT » Sat Jun 20, 2009 12:02 pm
bluementor wrote:
Stuart Kovinsky wrote:
asbestos wrote:At what speed was a car traveling when it had completed half of the distance of a trip?

(1) The car was traveling at an average speed of 65 miles per hour.

(2) The entire trip was 190 miles long and took 3 hours to complete.
To be honest, I don't even understand the question. What's the source?
This question is very similar to OG12 DS Q104 (pg 282). OA is E.

-BM-
The two major differences are:

(1) in Q104 in the OG, the average speed statement is worded unambiguously and is grammatically correct; and

(2) in Q104 in the OG, the two statements are complementary, not contradictory.

However, the correct answer still boils down to "it's almost impossible to calculate instantaneous speed, so choose (E)".
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