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# If a certain sample of data has a mean of 20.0 and a

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If a certain sample of data has a mean of 20.0 and a [#permalink]

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11 Apr 2012, 00:46
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If a certain sample of data has a mean of 20.0 and a standard deviation of 3.0, which of the following values is more than 2.5 standard deviations from the mean?

A. 12.0
B. 13.5
C. 17.0
D. 23.5
E. 26.5
[Reveal] Spoiler: OA

Last edited by Bunuel on 11 Apr 2012, 00:56, edited 1 time in total.
Edited the question
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Re: In a certain sample of data has mean = 20 and standard de [#permalink]

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11 Apr 2012, 00:55
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sapna44 wrote:
In a certain sample of data has mean = 20 and standard deviation = 3 , which of the following values is more than 2.5 standard deviation from mean ?

A. 12
B. 13.5
C. 17
D. 23.5
E. 26.5

If a certain sample of data has a mean of 20.0 and a standard deviation of 3.0, which of the following values is more than 2.5 standard deviations from the mean?

A. 12.0
B. 13.5
C. 17.0
D. 23.5
E. 26.5

Value is more than 2.5SD from the mean means that the distance between the mean and the value must be more than 2.5*SD=7.5. So the value must be either less than 20-7.5=12.5 or more than 20+7.5=27.5.

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Re: If a certain sample of data has a mean of 20.0 and a [#permalink]

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25 Feb 2013, 19:51
So from the mean means below the mean?
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Re: If a certain sample of data has a mean of 20.0 and a [#permalink]

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25 Feb 2013, 19:57
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fozzzy wrote:
So from the mean means below the mean?

No. 'Away from the mean' means either 'below the mean' or 'above the mean'.
(Bunuel has mentioned that the answer will be a value either less than 12.5 or greater than 27.5, in the post above.)
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Get started with Veritas Prep GMAT On Demand for $199 Veritas Prep Reviews Intern Joined: 18 Jan 2013 Posts: 2 Followers: 0 Kudos [?]: 0 [0], given: 7 Re: If a certain sample of data has a mean of 20.0 and a [#permalink] ### Show Tags 25 Feb 2013, 20:22 Hi, I thought that a SD of 2.5 from a MEAN of 20 would be a value dispersed 2.5 units away from 20, So I subtracted 2.5 from 20 and got the answer wrong. Can you please explain why did we multiply SD with 2.5? Cheers Veritas Prep GMAT Instructor Joined: 16 Oct 2010 Posts: 7125 Location: Pune, India Followers: 2134 Kudos [?]: 13650 [3] , given: 222 Re: If a certain sample of data has a mean of 20.0 and a [#permalink] ### Show Tags 25 Feb 2013, 20:40 3 This post received KUDOS Expert's post 1 This post was BOOKMARKED sanman wrote: Hi, I thought that a SD of 2.5 from a MEAN of 20 would be a value dispersed 2.5 units away from 20, So I subtracted 2.5 from 20 and got the answer wrong. Can you please explain why did we multiply SD with 2.5? Cheers There are two different things here: SD is 3. We need to find values which are 2.5 SD away from the mean. When we say that a value is at mean, it is 20. When we say that a value is 1 SD away from mean, it means the value is 3 away from mean (because 1 SD is 3). So it can be either 17 or 23. When we say that a value is 2 SD away from mean, it means that the value is 2*3 away from mean (because 2 SD is 6). So it can be either 14 or 26. When we say that a value is 2.5 SD away from mean, it means that the value is 2.5*3 away from mean. So it can be either 12.5 or 27.5. Since we want a value which is more than 2.5 SD away, the value must be less than 12.5 or greater than 27.5. _________________ Karishma Veritas Prep | GMAT Instructor My Blog Get started with Veritas Prep GMAT On Demand for$199

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Re: If a certain sample of data has a mean of 20.0 and a [#permalink]

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19 Nov 2013, 14:51
2.5 * 3 = 7.5

20 - 7.5 = 12.5
20 + 7.5 = 27.5

Limits: 12.5 and 27.5

Ans A (12 is out of the limits)
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Re: If a certain sample of data has a mean of 20.0 and a [#permalink]

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22 Nov 2014, 14:01
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Re: If a certain sample of data has a mean of 20.0 and a [#permalink]

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11 Mar 2016, 07:40
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Re: If a certain sample of data has a mean of 20.0 and a [#permalink]

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23 Jul 2016, 06:17
sapna44 wrote:
If a certain sample of data has a mean of 20.0 and a standard deviation of 3.0, which of the following values is more than 2.5 standard deviations from the mean?

A. 12.0
B. 13.5
C. 17.0
D. 23.5
E. 26.5

Range of SD will be = mean -2.4 SD + mean + 2.5 SD
Range = 12.5 to 27.5
The only value that falls outside the range is 12 which is lower than 12.5

A
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Re: If a certain sample of data has a mean of 20.0 and a   [#permalink] 23 Jul 2016, 06:17
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