Properties of Mean, Standard Deviation : GMAT Quantitative Section
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# Properties of Mean, Standard Deviation

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Properties of Mean, Standard Deviation [#permalink]

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08 Apr 2014, 07:10
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Hi Guys,

Have my gmat in less than 36 hours and would appreciate help on the following:

Standard Deviation and Mean for a set of numbers

How does each change if:
a. a certain number is added to all the numbers
b. a certain number is subtracted from all the numbers
c. a certain number is multiplied with all the numbers
d. all the numbers are divided by a certain number
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Re: Properties of Mean, Standard Deviation [#permalink]

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08 Apr 2014, 08:14
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brobeedle wrote:
Hi Guys,

Have my gmat in less than 36 hours and would appreciate help on the following:

Standard Deviation and Mean for a set of numbers

How does each change if:
a. a certain number is added to all the numbers
b. a certain number is subtracted from all the numbers
c. a certain number is multiplied with all the numbers
d. all the numbers are divided by a certain number

If we add or subtract a constant to each term in a set:
Mean will increase or decrease by the same constant.
SD will not change.

If we increase or decrease each term in a set by the same percent (multiply all terms by the constant):
Mean will increase or decrease by the same percent.
SD will increase or decrease by the same percent.

Questions on this concept to practice:
if-q-is-a-set-of-consecutive-integers-what-is-the-standard-151794.html
in-the-last-two-years-each-of-jeremy-s-six-children-grew-in-130614.html
during-an-experiment-some-water-was-removed-from-each-of-94166.html
set-a-consists-of-all-even-integers-between-2-and-110876.html
if-d-is-the-standard-deviation-x-y-and-z-what-is-the-stan-93979.html
what-is-sd-of-given-set-of-numbers-whose-average-is-104000.html
there-is-a-set-of-consecutive-even-integers-what-is-the-98877.html

Theory on Statistics and Sets problems: math-standard-deviation-87905.html

All DS Statistics and Sets problems to practice: search.php?search_id=tag&tag_id=34
All PS Statistics and Sets problems to practice: search.php?search_id=tag&tag_id=55

Hope this helps.
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Re: Properties of Mean, Standard Deviation [#permalink]

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08 Apr 2014, 23:27
Thanks Bunuel, so am I right to say that if all the terms are divided by the same constant, the effect is not linear - i.e., cannot be determined unless we calculate the st.dev of the new set as well?
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Re: Properties of Mean, Standard Deviation [#permalink]

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09 Apr 2014, 01:16
brobeedle wrote:
Thanks Bunuel, so am I right to say that if all the terms are divided by the same constant, the effect is not linear - i.e., cannot be determined unless we calculate the st.dev of the new set as well?

No.

Multiplying is the same as dividing: for example, dividing by 2 is the same as multiplying by 1/2.

If we increase or decrease each term in a set by the same percent (multiply all terms by the constant):
Mean will increase or decrease by the same percent.
SD will increase or decrease by the same percent.

Thus the above holds true for dividing as well.

Hope it's clear.
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Re: Properties of Mean, Standard Deviation [#permalink]

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09 Apr 2014, 19:10
Thank you! Clear now

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Re: Properties of Mean, Standard Deviation   [#permalink] 09 Apr 2014, 19:10
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