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# QOTD #8 The distribution of the numbers of hours that

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Joined: 07 Jun 2014
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QOTD #8 The distribution of the numbers of hours that [#permalink]  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

Practice Questions
Question: 18
Page: 153

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

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Sandy
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GMAT Club Legend
Joined: 07 Jun 2014
Posts: 4704
GRE 1: Q167 V156
WE: Business Development (Energy and Utilities)
Followers: 90

Kudos [?]: 1596 [0], given: 373

Re: QOTD #8 The distribution of the numbers of hours that [#permalink]  14 Aug 2016, 07:09
Expert's post
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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Sandy
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Re: QOTD #8 The distribution of the numbers of hours that [#permalink]  11 Dec 2016, 14:53
1
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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
GMAT Club Legend
Joined: 07 Jun 2014
Posts: 4704
GRE 1: Q167 V156
WE: Business Development (Energy and Utilities)
Followers: 90

Kudos [?]: 1596 [1] , given: 373

Re: QOTD #8 The distribution of the numbers of hours that [#permalink]  11 Dec 2016, 16:28
1
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Expert's post
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:

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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Sandy
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Re: QOTD #8 The distribution of the numbers of hours that [#permalink]  13 Dec 2016, 10:53
many many many thnxxxx
i got it now
Intern
Joined: 24 May 2016
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Kudos [?]: 7 [0], given: 22

Re: QOTD #8 The distribution of the numbers of hours that [#permalink]  13 Dec 2016, 10:53
many many many thnxxxx
i got it now
Intern
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Re: QOTD #8 The distribution of the numbers of hours that [#permalink]  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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