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A list of numbers has a mean of 8 and a standard deviation of 2.5. If

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A list of numbers has a mean of 8 and a standard deviation of 2.5. If  [#permalink]

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New post 03 Jun 2019, 23:32
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A
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D
E

Difficulty:

  15% (low)

Question Stats:

69% (00:28) correct 31% (00:57) wrong based on 36 sessions

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Concentration: Sustainability, Marketing
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Re: A list of numbers has a mean of 8 and a standard deviation of 2.5. If  [#permalink]

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New post 04 Jun 2019, 00:52
Bunuel wrote:
A list of numbers has a mean of 8 and a standard deviation of 2.5. If x is a number in the list that is 2 standard deviations above the mean, what is the value of x ?

A. 10
B. 11
C. 12
D. 13
E. 14


value = 8+2*2.5
13
IMO D
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Re: A list of numbers has a mean of 8 and a standard deviation of 2.5. If  [#permalink]

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New post 04 Jun 2019, 06:00
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Top Contributor
1
Bunuel wrote:
A list of numbers has a mean of 8 and a standard deviation of 2.5. If x is a number in the list that is 2 standard deviations above the mean, what is the value of x ?

A. 10
B. 11
C. 12
D. 13
E. 14

---------ASIDE----------------------------
A little extra background on standard deviations above and below the mean

If, for example, a set has a standard deviation of 4, then:
1 standard deviation = 4
2 standard deviations = 8
3 standard deviations = 12
1.5 standard deviations = 6
0.25 standard deviations = 1
etc


So, if the mean of a set is 9, and the standard deviation is 4, then:
2 standard deviations ABOVE the mean = 17 [since 9 + 2(4) = 17]
1.5 standard deviations BELOW the mean = 3 [since 9 - 1.5(4) = 3]
3 standard deviations ABOVE the mean = 21 [since 9 + 3(4) = 21]
etc.
-------------------------------------------

A list of numbers has a mean of 8 and a standard deviation of 2.5. If x is a number in the list that is 2 standard deviations above the mean, what is the value of x ?
x = 8 + 2(2.5)
= 8 + 5
= 13

Answer: D

Cheers,
Brent
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Re: A list of numbers has a mean of 8 and a standard deviation of 2.5. If  [#permalink]

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New post 09 Jun 2019, 17:59
Bunuel wrote:
A list of numbers has a mean of 8 and a standard deviation of 2.5. If x is a number in the list that is 2 standard deviations above the mean, what is the value of x ?

A. 10
B. 11
C. 12
D. 13
E. 14



2 standard deviations above the mean is:

2 x 2.5 + 8 = 5 + 8 = 13, so the number is 13.

Answer: D
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Re: A list of numbers has a mean of 8 and a standard deviation of 2.5. If   [#permalink] 09 Jun 2019, 17:59

A list of numbers has a mean of 8 and a standard deviation of 2.5. If

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