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Properties of Mean, Standard Deviation [#permalink]
08 Apr 2014, 07:10

1

This post was BOOKMARKED

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

Re: Properties of Mean, Standard Deviation [#permalink]
08 Apr 2014, 08:14

2

This post received KUDOS

Expert's post

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.

Re: Properties of Mean, Standard Deviation [#permalink]
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?

Re: Properties of Mean, Standard Deviation [#permalink]
09 Apr 2014, 01:16

Expert's post

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.

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