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# What is the standard deviation of Q, a set of consecutive

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What is the standard deviation of Q, a set of consecutive [#permalink]

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19 Aug 2008, 20:42
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What is the standard deviation of Q, a set of consecutive integers?

(1) Q has 11 members.

(2) The median value of set Q is 10.

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Re: Standard Deviation DS question: [#permalink]

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19 Aug 2008, 21:35
gary789 wrote:
What is the standard deviation of Q, a set of consecutive integers?

(1) Q has 11 members.

(2) The median value of set Q is 10.

IMO A)

Statement 1) should be suff. according to rule where if certain number is added or subtracted with all elements of set then standard deviation remains same.

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Re: Standard Deviation DS question: [#permalink]

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19 Aug 2008, 22:30
D since the numbers are consecutive.

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Re: Standard Deviation DS question: [#permalink]

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19 Aug 2008, 22:42
D?

two sets {9,10,11} and {7,8,9,10,11,12,13} have median 10 but SD are different for these two. Hence (2) is NOT SUFF

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Re: Standard Deviation DS question: [#permalink]

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19 Aug 2008, 23:58
gary789 wrote:
What is the standard deviation of Q, a set of consecutive integers?

(1) Q has 11 members.

(2) The median value of set Q is 10.

1) is suff

sd=sqrt((a-x)^2)/n)
where n= no of elements =11
and given that they are consecutive so middle no will be the average so
sd=2(1^2+2^2+3^2+4^2+5^2)/11

the numbers are not required

to explain clearly take numbers as n,n+1,..........,n+10
avg=n+4

substitute in the formula of SD ull get the ans

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Re: Standard Deviation DS question: [#permalink]

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28 Aug 2008, 12:26
gary789 wrote:
What is the standard deviation of Q, a set of consecutive integers?

(1) Q has 11 members.
(2) The median value of set Q is 10.

A.

1: no (11) of consecutive integers is enough to find the SD. suff
2: median doesnot work. median with different set of consecutive integers have different SD>. nsf..
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Re: Standard Deviation DS question: [#permalink]

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28 Aug 2008, 12:58
A.

Statement 1 If numbers are consecutive then the median = mean,plus the difference between the mean and each number is known, hence we can compute Sd

Statement 2: is insuff because the numbers could all be 10, they could be all close to 10, they could be consecutive, they could be al over the place, hence there is no way to calculate the SD

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Re: Standard Deviation DS question:   [#permalink] 28 Aug 2008, 12:58
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