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The members of the newest recruiting class of a certain

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Intern
Joined: 25 May 2008
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The members of the newest recruiting class of a certain [#permalink]  29 May 2008, 12:39
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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 recruits have to retest?

(1) There are 500 recruits in the class.

(2) 10 recruits score 82 or higher.

I think it is C.
Director
Joined: 23 Sep 2007
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Re: DS - Standard deviation [#permalink]  29 May 2008, 17:01
This question is straight out of the princeton review math bin 4 question #3. The answer is C, but it requires you to know that 4.2% of the population is more than 2 SD away from the mean, and 27.2% of the population is 2 SD from the mean.

If you have the book, then you should know the explanation. But I don't think the GMAT requires you to know the exact percentages of the population distribution.

If you want another stupid princeton review math question, try bin 4 question #20.
Director
Joined: 14 Jan 2007
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Re: DS - Standard deviation [#permalink]  29 May 2008, 17:07
Should be 'C'.

For the normal distribution, one standard deviation( σ )accounts for about 68% of the set. we have to find out the σ.

stmt1: recruits 500 does not give the suff info.

stmt2: in suff

taking them together:
2% score >= 82
this means 2 σ =82-72 =10
σ=5
Re: DS - Standard deviation   [#permalink] 29 May 2008, 17:07
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