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# Standard deviation and mean.

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Intern
Joined: 08 Mar 2010
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Standard deviation and mean. [#permalink]  08 Mar 2010, 01:37
00:00

Difficulty:

5% (low)

Question Stats:

83% (01:18) correct 17% (00:00) wrong based on 7 sessions
The arithmetic mean and standard deviation of a certain normal distribution are 13.5 and 1.5, respectively. What value is exactly 2 standard deviations from the mean?

A) 10.5
B) 11
C) 11.5
D) 12
E) 12.5

Thanks
Manager
Joined: 29 Oct 2009
Posts: 203
Concentration: General Management, Sustainability
WE: Consulting (Computer Software)
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Re: Standard deviation and mean. [#permalink]  08 Mar 2010, 07:23
Mean = 13.5
Two standard deviations is 1.5 + 1.5 = 3.0

There could be two calues for this.
Mean + two standard deviations = 16.5
Mean - Two standard deviations = 10.5

What is the OA?
Senior Manager
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Re: Standard deviation and mean. [#permalink]  08 Mar 2010, 07:28
ronny13 wrote:
The arithmetic mean and standard deviation of a certain normal distribution are 13.5 and 1.5, respectively. What value is exactly 2 standard deviations from the mean?

A) 10.5
B) 11
C) 11.5
D) 12
E) 12.5

Thanks

13.5-2(1.5) or 13.5_2(1.5)
10.5 or 16.5

hence A.
Intern
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Re: Standard deviation and mean. [#permalink]  08 Mar 2010, 07:32
Agree with A

Two deviations in both directions : 13.5 + 2( 1.5) = 16.5

and 13.5 - 2(1.5) = 10.5
Manager
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Re: Standard deviation and mean. [#permalink]  11 Jun 2011, 13:09
A..

It can be either 13.5 + 2(1.5) = 16.5

OR

13.5 - 2(1.5) = 10.5

Hence A

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Manager
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Re: Standard deviation and mean. [#permalink]  11 Jun 2011, 13:11
Why use the word "normal distribution " in the question? Does it add any meaning?
The question can be solved without it.

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Re: Standard deviation and mean. [#permalink]  11 Jun 2011, 15:47
puneetj wrote:
Why use the word "normal distribution " in the question? Does it add any meaning?
The question can be solved without it.

The word 'normal' could certainly be removed without changing the question in any way. The distribution doesn't need to have any special properties here.

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Director
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Re: Standard deviation and mean. [#permalink]  11 Jun 2011, 16:37
AM = 13.5
SD = 1.5

the value that's 2 SD's away from the mean could be either 13.5+2(1.5) or 13.5-2(1.5)

i.e 13.5+3 or 13.5-3 = 16.5 or 10.5

Manager
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Re: Standard deviation and mean. [#permalink]  11 Jun 2011, 17:18
IanStewart wrote:
puneetj wrote:
Why use the word "normal distribution " in the question? Does it add any meaning?
The question can be solved without it.

The word 'normal' could certainly be removed without changing the question in any way. The distribution doesn't need to have any special properties here.

Thanks for the confirmation Ian

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Re: Standard deviation and mean.   [#permalink] 11 Jun 2011, 17:18
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