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M is a certain set of numbers with an average (arithmetic

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M is a certain set of numbers with an average (arithmetic  [#permalink]

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New post 17 Jul 2014, 06:02
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Question Stats:

69% (01:59) correct 31% (01:57) wrong based on 233 sessions

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M is a certain set of numbers with an average (arithmetic mean) of 10 and a standard deviation of 2.5. Q is a subset of M consisting of 5 terms. Exactly 80% of the numbers in Q are located within 2 standard deviations from the average of M. Which of the following could Q be?

A. {3, 4, 5, 10, 14}
B. {3, 6, 7, 10, 12}
C. {3, 5, 5, 10, 16}
D. {1, 5, 7, 10, 18}
E. {5, 6, 7, 10, 12}
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M is a certain set of numbers with an average (arithmetic  [#permalink]

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New post 17 Jul 2014, 06:16
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goodyear2013 wrote:
M is a certain set of numbers with an average (arithmetic mean) of 10 and a standard deviation of 2.5. Q is a subset of M consisting of 5 terms. Exactly 80% of the numbers in Q are located within 2 standard deviations from the average of M. Which of the following could Q be?

A. {3, 4, 5, 10, 14}
B. {3, 6, 7, 10, 12}
C. {3, 5, 5, 10, 16}
D. {1, 5, 7, 10, 18}
E. {5, 6, 7, 10, 12}


Exactly 80% of the numbers in Q, so 4 out of 5 numbers are from 10 - 2*{SD} = 5 to 10 + 2*{SD} = 15.

A. {3, 4, 5, 10, 14} --> only 3 numbers are in this range. Discard.
B. {3, 6, 7, 10, 12} --> 4 numbers are in this range. OK.
C. {3, 5, 5, 10, 16} --> only 3 numbers are in this range. Discard.
D. {1, 5, 7, 10, 18} --> only 3 numbers are in this range. Discard.
E. {5, 6, 7, 10, 12} --> all 5 numbers are in this range. Discard.

Answer: B.

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Re: M is a certain set of numbers with an average (arithmetic  [#permalink]

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New post 30 Oct 2018, 06:11
10 - 2*{SD} = 5 to 10 + 2*{SD} = 15

please explain this .

Thanks
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Re: M is a certain set of numbers with an average (arithmetic   [#permalink] 30 Oct 2018, 06:11
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