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Re: Set A {3,3,3,4,5,5,5} has a standard deviation of 1. [#permalink]
02 Sep 2012, 20:16

1

This post received KUDOS

Variance = (sum of (squares of difference of each number from mean )) / total number of numbers Standard deviation = sqrt Variance

When we multiply all the numbers by something then while calculating the standard deviation we can take out that thing common new standard deviation will be equal to value by which we multiplied all the number* old standard deviation.

Ex: Suppose we have 4 entries a,b,c,d and suppose the mean is m Then standard deviation = sqrt { { (a-m)^2 + (b-m)^2 + (c-m)^2 + (d-m)^2 } / 4 }

Now we multiply all the number by 4 so the new set will be 4a, 4b, 4c, 4d the new mean will be 4a + 4b+ 4c+ 4d /4 = 4 *( (a+b+c+d) /4 ) = 4m

Re: Set A {3,3,3,4,5,5,5} has a standard deviation of 1. [#permalink]
02 Sep 2012, 20:38

2

This post received KUDOS

Smita04 wrote:

Set A {3,3,3,4,5,5,5} has a standard deviation of 1. What will the standard deviation be if every number in the set is multiplied by 4?

A)1 B)2 C)4 D)8 E)16

Points to remember - 1. If one Add/Subtract the same amont from every term in a set, SD doesn't change. 2. If one Multiply/Divide every term by the same number in a set, SD changes by same number.

Hence the answer to the above question is C. Cheers! _________________

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Re: Set A {3,3,3,4,5,5,5} has a standard deviation of 1. [#permalink]
03 Oct 2014, 06:09

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Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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