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Math Expert V
Joined: 02 Sep 2009
Posts: 64322
A list of numbers has a mean of 8 and a standard deviation of 2.5. If  [#permalink]

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Difficulty:   15% (low)

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

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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

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GMAT Club Legend  V
Joined: 18 Aug 2017
Posts: 6324
Location: India
Concentration: Sustainability, Marketing
GPA: 4
WE: Marketing (Energy and Utilities)
Re: A list of numbers has a mean of 8 and a standard deviation of 2.5. If  [#permalink]

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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
GMAT Club Legend  V
Joined: 11 Sep 2015
Posts: 4889
GMAT 1: 770 Q49 V46
Re: A list of numbers has a mean of 8 and a standard deviation of 2.5. If  [#permalink]

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2
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

Cheers,
Brent
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Target Test Prep Representative V
Status: Founder & CEO
Affiliations: Target Test Prep
Joined: 14 Oct 2015
Posts: 10683
Location: United States (CA)
Re: A list of numbers has a mean of 8 and a standard deviation of 2.5. If  [#permalink]

### Show Tags

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.

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# Scott Woodbury-Stewart

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If you find one of my posts helpful, please take a moment to click on the "Kudos" button. 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  