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Question involving normal distribution concept

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by Svedankae » Wed Aug 12, 2009 3:54 am
I found this question in the Princeton Review book but it seems far off from real GMAT material.... or is this something to expect on the test?

The members of the newest recruiting class of a certain military organization are taking their physical conditioning test, and those who score in the bottom 16% will have to retest. If the scores are normally distributed and have an arithmetic mean of 72, what is the score at or below which the recruits will have to retest?

(1) There are 500 recruits in the class

(2) 10 recruits scored 82 or higher
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Source: — Data Sufficiency |
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Re: Question involving normal distribution concept

by life is a test » Wed Aug 12, 2009 7:33 am
Svedankae wrote:I found this question in the Princeton Review book but it seems far off from real GMAT material.... or is this something to expect on the test?

The members of the newest recruiting class of a certain military organization are taking their physical conditioning test, and those who score in the bottom 16% will have to retest. If the scores are normally distributed and have an arithmetic mean of 72, what is the score at or below which the recruits will have to retest?

(1) There are 500 recruits in the class

(2) 10 recruits scored 82 or higher
This is a data sufficiency question...I am assuming the answer is E since you have not been given the standard deviation?

I have tried to capture in the attachment all that i believe you need to know on the subj....(area in red corresponds to bottom 16%).
Attachments
normal distribution.JPG
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by Svedankae » Wed Aug 12, 2009 8:08 am
ah so i am supposed to know that distribution? ...interesting, thanks.


and btw in that case, the answer is not E because we do know the standard deviation since 10 recruits resemble 2%...
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by life is a test » Wed Aug 12, 2009 8:11 pm
Svedankae wrote:ah so i am supposed to know that distribution? ...interesting, thanks.


and btw in that case, the answer is not E because we do know the standard deviation since 10 recruits resemble 2%...
How did you derive the 2%?

the s.d. is a spread measure, uness we know each of the values used to calculate the mean, we will not be able to calculate the overall spread of the nums...pls correct me if I am wrong.
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2%

by wneo » Thu Aug 13, 2009 8:07 am
10 recruits out of 500 is 2%.
Mean is 72, 2 sd is 82. I will assume sd is 5.
Please correct me if I am wrong.

life is a test wrote:
Svedankae wrote:ah so i am supposed to know that distribution? ...interesting, thanks.


and btw in that case, the answer is not E because we do know the standard deviation since 10 recruits resemble 2%...
How did you derive the 2%?

the s.d. is a spread measure, uness we know each of the values used to calculate the mean, we will not be able to calculate the overall spread of the nums...pls correct me if I am wrong.
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by Ian Stewart » Sat Aug 15, 2009 5:00 pm
You do not need to know anything about the normal distribution for the GMAT (it's an infinite distribution, and the GMAT only tests finite statistics). As for the question in the original post, not only is it an unrealistic GMAT question, it is also deeply mathematically flawed, as I explained in some detail the last time this question appeared on this forum. Best just to move on.
For online GMAT math tutoring, or to buy my higher-level Quant books and problem sets, contact me at ianstewartgmat at gmail.com

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