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QOTD #8 The distribution of the numbers of hours that

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QOTD #8 The distribution of the numbers of hours that [#permalink] New post 14 Aug 2016, 07:06
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Question Stats:

75% (00:35) correct 25% (00:29) wrong based on 16 sessions
The distribution of the numbers of hours that students at a certain college studied for final exams has a mean of 12 hours and a standard deviation of 3 hours. Which of the following numbers of hours are within 2 standard deviations of the mean of the distribution?

Indicate all such numbers.


A. 2
B. 5
C. 10
D. 14
E. 16
F. 20


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Question: 18
Page: 153


[Reveal] Spoiler: OA
C, D, E
[Reveal] Spoiler: OA

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GMAT Club Legend
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Joined: 07 Jun 2014
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GRE 1: Q167 V156
WE: Business Development (Energy and Utilities)
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Kudos [?]: 1596 [0], given: 373

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Re: QOTD #8 The distribution of the numbers of hours that [#permalink] New post 14 Aug 2016, 07:09
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Explanation

Given that the mean of the distribution is 12 hours and the standard deviation is 3 hours, the numbers of hours within 2 standard deviations of the mean are all numbers of hours between 12 – 2(3), or 6, and 12 + 2(3), or 18. Thus the correct answer consists of Choices C, D, and E.
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Re: QOTD #8 The distribution of the numbers of hours that [#permalink] New post 11 Dec 2016, 14:53
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Sorry i can't understand this answer by any-mean
if there is more clarification it would be great
thnx a lot
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GMAT Club Legend
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Re: QOTD #8 The distribution of the numbers of hours that [#permalink] New post 11 Dec 2016, 16:28
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You need to familiarize yourself with standard deviation and mean values in order to attempt this problem.

The normal distribution is a pattern for the distribution of data which follows a bell-shaped curve. The normal distribution is called normal because the data points are concentrated in the center near the mean, the data does not usually contain extreme values, and the probability of deviations of the data points from the mean are (nearly) identical in either direction. Graphically, the normal distribution looks like the following:

Image

Where 0 is the mean, and \(0+ \sigma\) and \(0- \sigma\) designate one standard deviation greater and less than the mean. The percentage values in the above figure indicate what percentage of the data fall into that region.
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Re: QOTD #8 The distribution of the numbers of hours that [#permalink] New post 13 Dec 2016, 10:53
many many many thnxxxx
i got it now
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Re: QOTD #8 The distribution of the numbers of hours that [#permalink] New post 13 Dec 2016, 10:53
many many many thnxxxx
i got it now
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Re: QOTD #8 The distribution of the numbers of hours that [#permalink] New post 04 Sep 2018, 19:44
here the mean is 12.
Standard deviation is 3. 2 standard deviations meaning the distance between the mean and the numbers will be 6 . so any option between 6 to 18 will be answer to this question.
so the answer is C, D, E
Re: QOTD #8 The distribution of the numbers of hours that   [#permalink] 04 Sep 2018, 19:44
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