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# from Veritas ProjectGMAT. One of their tips with no example

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CEO
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from Veritas ProjectGMAT. One of their tips with no example [#permalink]

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15 May 2007, 19:45
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

from Veritas ProjectGMAT. One of their tips with no example shown...

"Adding or subtracting a constant from each element in the set has no effect on the standard deviation"

Can someone elaborate on this?
Director
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15 May 2007, 19:52
bmwhype2 wrote:
from Veritas ProjectGMAT. One of their tips with no example shown...

"Adding or subtracting a constant from each element in the set has no effect on the standard deviation"

Can someone elaborate on this?

suppose the value of x are: 10, 11, 13, 15, and 20
now you deduct 5 from each, then x values are: 5, 6, 8, 10 and 15
now you add 5 on each, then values of x are: 15, 16, 18, 20 and 25

the sd is 3.96 in all cases.
CEO
Joined: 21 Jan 2007
Posts: 2747
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Kudos [?]: 938 [0], given: 4

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15 May 2007, 19:53
nevermind. figured it out...

set a (1,2,3,4,5,) Standard deviation of 1
set b (5,6,7,8,9) all terms n+5 . standard deviation of 1

therefore, sd is the same.
Manager
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15 May 2007, 22:26
This happens coz if we subtract or add some constant number from a set of numbers then the average also decreases or increases respectively by same figure thus keeping the difference of numbers and average constant.
CEO
Joined: 21 Jan 2007
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15 May 2007, 22:37
apache wrote:
This happens coz if we subtract or add some constant number from a set of numbers then the average also decreases or increases respectively by same figure thus keeping the difference of numbers and average constant.

yea. just shifting the entire set (all the elements) by the same ratio or amount.
15 May 2007, 22:37
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