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Standard deviation and mean.

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Standard deviation and mean. [#permalink] New post 08 Mar 2010, 02:37
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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

Can you please help me out on this.

Thanks
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Re: Standard deviation and mean. [#permalink] New post 08 Mar 2010, 08:23
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

Answer choice has 10.5 and so A is the answer.

What is the OA?
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Re: Standard deviation and mean. [#permalink] New post 08 Mar 2010, 08:28
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

Can you please help me out on this.
Thanks

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

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

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

and 13.5 - 2(1.5) = 10.5
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Re: Standard deviation and mean. [#permalink] New post 11 Jun 2011, 14:09
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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Re: Standard deviation and mean. [#permalink] New post 11 Jun 2011, 14:11
Why use the word "normal distribution " in the question? Does it add any meaning?
The question can be solved without it.

Math experts ..please clarify
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Re: Standard deviation and mean. [#permalink] New post 11 Jun 2011, 16:47
puneetj wrote:
Why use the word "normal distribution " in the question? Does it add any meaning?
The question can be solved without it.

Math experts ..please clarify


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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Re: Standard deviation and mean. [#permalink] New post 11 Jun 2011, 17:37
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

Answer is A.
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Re: Standard deviation and mean. [#permalink] New post 11 Jun 2011, 18:18
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.

Math experts ..please clarify


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, 18:18
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