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

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Manager
Joined: 05 Jan 2006
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What is the standard deviation of Q, a set of consecutive [#permalink]  27 May 2006, 01:47
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What is the standard deviation of Q, a set of consecutive integers?

I) Q has 21 members
II) The median value of set Q is 20

Enjoy!!
Senior Manager
Joined: 09 Mar 2006
Posts: 445
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A it is

A) since those integers are consequtive , you don't have to know the average to find the differences. SUFFICIENT

B) the number of integers in the set is not known, so insuff.
Senior Manager
Joined: 15 Mar 2005
Posts: 421
Location: Phoenix
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Re: A good one (DS Question) [#permalink]  27 May 2006, 10:35
x242222 wrote:
What is the standard deviation of Q, a set of consecutive integers?

I) Q has 21 members
II) The median value of set Q is 20

Enjoy!!

(I)
Looking at the formula to calculate SD, Av = 10th number.
Therefore, the dfferences are 10, 9, 8, .., 0, ... -8, -10. (note that this is standard)
Since the magnitude of the numbers does not enter the calculation anymore, the SD is independent of what numbers are chosen, as long as they're consecutive 21 numbers. Sufficient.
(II) This doesn't tell us the dispersion of individual data, and hence unable to calculate SD with certainly. Insufficient.

Thus A
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Director
Joined: 10 Oct 2005
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Location: US
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yeah since the difference between successive number is same SD will be same irrespective value of integer
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