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GRE Prep Club Legend  Joined: 07 Jun 2014
Posts: 4857
GRE 1: Q167 V156 WE: Business Development (Energy and Utilities)
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QOTD #8 The distribution of the numbers of hours that [#permalink]
Expert's post 00:00

Question Stats: 79% (00:35) correct 20% (00:30) wrong based on 24 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

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Sandy
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GRE Prep Club Legend  Joined: 07 Jun 2014
Posts: 4857
GRE 1: Q167 V156 WE: Business Development (Energy and Utilities)
Followers: 112

Kudos [?]: 1856 , given: 397

Re: QOTD #8 The distribution of the numbers of hours that [#permalink]
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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Kudos [?]: 8  , given: 22

Re: QOTD #8 The distribution of the numbers of hours that [#permalink]
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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 GRE Prep Club Legend  Joined: 07 Jun 2014
Posts: 4857
GRE 1: Q167 V156 WE: Business Development (Energy and Utilities)
Followers: 112

Kudos [?]: 1856  , given: 397

Re: QOTD #8 The distribution of the numbers of hours that [#permalink]
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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Intern Joined: 24 May 2016
Posts: 33
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Kudos [?]: 8 , given: 22

Re: QOTD #8 The distribution of the numbers of hours that [#permalink]
many many many thnxxxx
i got it now
Intern Joined: 24 May 2016
Posts: 33
Followers: 0

Kudos [?]: 8 , given: 22

Re: QOTD #8 The distribution of the numbers of hours that [#permalink]
many many many thnxxxx
i got it now
Intern Joined: 10 Jun 2018
Posts: 32
Followers: 0

Kudos [?]: 15 , given: 4

Re: QOTD #8 The distribution of the numbers of hours that [#permalink]
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
Manager Joined: 22 Jul 2018
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Kudos [?]: 10 , given: 42

Re: QOTD #8 The distribution of the numbers of hours that [#permalink]
Hi I have one query here.
As standard deviation changed from 3 to 2, then the mean value also changes? If yes, then how to calculate. Please explain.

My understanding is, Previous mean value is 12 and SD is 3. According to this data, i calculated the value of values as below
mean + SD = 15
mean - SD = 9
mean + 2(SD) = 18
mean -2(SD)= 6 Re: QOTD #8 The distribution of the numbers of hours that   [#permalink] 01 Dec 2018, 06:19
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