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Math: Standard Deviation

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Re: Math: Standard Deviation [#permalink]

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New post 17 May 2015, 23:12
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Re: Math: Standard Deviation [#permalink]

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New post 03 Sep 2015, 11:25
walker wrote:
GMATMadeeasy wrote:
...or it means that Standard deviation of any 39 consecitive even integers will be same as they are equally distributed with respect to the avarge ?


Exactly. Let's look at simple example,

{4,6,8} and {1004,1006,1008} they have the same STD because all elements of second set are shifted by constant number 1000.


thanks for the explanation but shouldn't the number here be "2" instead of "1000"?

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Re: Math: Standard Deviation [#permalink]

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New post 24 Dec 2015, 10:12
I have a question related to SD.

if a number is exactly the mean, is it considered within 1 SD from the mean?

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Re: Math: Standard Deviation [#permalink]

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New post 24 Dec 2015, 11:41

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Re: Math: Standard Deviation [#permalink]

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New post 24 Dec 2015, 17:51
mvictor wrote:
I have a question related to SD.

if a number is exactly the mean, is it considered within 1 SD from the mean?


Yes because technically en element = mean of the set will be at exactly 0 Standard deviations from the mean and as such it will be within 1 or 2 or 3 etc SDs.
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Re: Math: Standard Deviation [#permalink]

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New post 23 Aug 2016, 18:25
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Example #3
Q: Standard deviation of set {23,31,76,45,16,55,54,36}{23,31,76,45,16,55,54,36} is 18.3. How many elements are 1 standard deviation above the mean?
Solution: Let's find mean: \m=23+31+76+45+16+55+54+368=42\m=23+31+76+45+16+55+54+368=42
Now, we need to count all numbers greater than 42+18.3=60.3. It is one number - 76. The answer is 1.


Kindly correct me if I am wrong
I think elements that are 1 standard deviation (d) above the mean(m) = elements within 'm' and 'm+d'
so shouldn't it be elements within 42 and 60.3?
Thanks in advance.:)

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Re: Math: Standard Deviation [#permalink]

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I have a question regarding standard deviation. I am unsure about how to solve standard deviation's comparing sets questions. For example: If I am given a set and asked as to what of the following options have the standard deviation closest to the one given in question. Questions such as

Which of the following options have the standard deviation closest to the standard deviation to set A = [10,15,20,25,30]

A [30,40,50,60,70]
B [5,15,25,35,45]
C [20, 35, 50, 65, 80]
D [ -20,-10,0,10,20]
E [24, 40, 56, 80,96]

How do I compare these options with the one given in the question?

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Re: Math: Standard Deviation [#permalink]

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New post 25 Jun 2017, 06:12
keats wrote:
I have a question regarding standard deviation. I am unsure about how to solve standard deviation's comparing sets questions. For example: If I am given a set and asked as to what of the following options have the standard deviation closest to the one given in question. Questions such as

Which of the following options have the standard deviation closest to the standard deviation to set A = [10,15,20,25,30]

A [30,40,50,60,70]
B [5,15,25,35,45]
C [20, 35, 50, 65, 80]
D [ -20,-10,0,10,20]
E [24, 40, 56, 80,96]

How do I compare these options with the one given in the question?


Hi keats,
In the set A gap between consecutive terms is 5. Now, check for all the options.

(A) Gap 10
(B) Gap 10
(C) Gap 15
(D) Gap 10
(E) Gap 16,16,24, and 16.

There is no unique answer to this question. Option (A), (B) and (D) will have closest Standard Deviation (SD) to the Set A.

You don't need to compute the SD for all the options.

Some more information we can deduce from the above-given data set without computing SD.

=> Option (A), (B), and (D) will have the same SD. Because SD doesn't change with addition or subtraction of a constant number.

=> Option (E) will have highest SD among all.

Hope this helps.

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Re: Math: Standard Deviation [#permalink]

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New post 17 Sep 2017, 03:36
Shouldn't the divisor be (N-1) for the variance and the standard variation

--> variance=∑(xi−xav)^2/(N-1)

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Re: Math: Standard Deviation [#permalink]

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Re: Math: Standard Deviation   [#permalink] 17 Sep 2017, 03:42

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