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The mean and the standard deviation of the 8 numbers shown

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The mean and the standard deviation of the 8 numbers shown [#permalink] New post 29 Jul 2010, 22:39
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D
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Question Stats:

89% (01:48) correct 11% (02:10) wrong based on 57 sessions
9.4 , 9.9 , 9.9 , 9.9 , 10.0 , 10.2 , 10.2 , 10.5
The mean and the standard deviation of the 8 numbers shown above is 10 and 0.3 respectively. What percent of the 8 numbers are within 1 standard deviation of the mean?

A. 90%
B. 85%
C. 80%
D. 75%
E. 70%
[Reveal] Spoiler: OA

Last edited by Bunuel on 19 Feb 2012, 21:19, edited 1 time in total.
Edited the question and added the OA
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Re: P.S [#permalink] New post 29 Jul 2010, 23:13
Expert's post
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Question should be:

9.4 , 9.9 , 9.9 , 9.9 , 10.0 , 10.2 , 10.2 , 10.5
The mean and the standard deviation of the 8 numbers shown above is 10 and 0.3 respectively. What percent of the 8 numbers are within 1 standard deviation of the mean?


A. 90%
B. 85%
C. 80%
D. 75%
E. 70%

"Within 1 standard deviation of the mean" - means in the range {mean-1*sd; mean+1*sd} = {10-*0.3; 10+0.3} = {9.7; 10.3}.

From the 8 listed numbers, 6 are within this range so 6/8=75%.

Answer: D.
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Re: The mean and the standard deviation of the 8 numbers shown [#permalink] New post 19 Jun 2014, 03:48
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Re: The mean and the standard deviation of the 8 numbers shown   [#permalink] 19 Jun 2014, 03:48
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