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# PS questions about standard deviation.

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Intern
Status: Don't watch the clock,Do what it does, Keep Going.
Joined: 10 Jan 2017
Posts: 46
Re: PS questions about standard deviation. [#permalink]

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13 Oct 2017, 08:37
Bunuel would you please provide the OA for the given problems
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Joined: 02 Sep 2009
Posts: 44320
Re: PS questions about standard deviation. [#permalink]

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13 Oct 2017, 08:43
adil123 wrote:
Bunuel would you please provide the OA for the given problems

Please check the discussion on previous pages. You'll find OA's as well as solutions.
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Joined: 30 Apr 2017
Posts: 87
Re: PS questions about standard deviation. [#permalink]

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14 Oct 2017, 01:46
Bunuel wrote:
casanjiv wrote:
9. E is a collection of four odd integers and the greatest difference between any two integers in E is 4. The standard deviation of E must be one of how many numbers?
(A) 3
(B) 4
(C) 5
(D) 6
(E) 7

Question says greatest difference between any two integers in E is 4, how come the range is 4.

"The greatest difference between any two integers in E is 4" does not mean that if you pick any two integers their difference will be 4. It means that the greatest difference you can get from any pair of integers from E is 4. Since the range is the difference between the largest and the smallest elements of a set, then 4 must be the range of E.

Check this for more on this question: http://gmatclub.com/forum/ps-questions- ... ml#p810657 (or: http://gmatclub.com/forum/e-is-a-collec ... ml#p769204).

Hope it helps.

Bunuel thank you for such a classified question,I could cover SD topic, but unfortuantely I was just wrong about this question.
Why we don't assume negative numbers? such as {-1,-1,1,3} etc...??
Math Expert
Joined: 02 Sep 2009
Posts: 44320
Re: PS questions about standard deviation. [#permalink]

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14 Oct 2017, 01:53
soodia wrote:
Bunuel wrote:
casanjiv wrote:
9. E is a collection of four odd integers and the greatest difference between any two integers in E is 4. The standard deviation of E must be one of how many numbers?
(A) 3
(B) 4
(C) 5
(D) 6
(E) 7

Question says greatest difference between any two integers in E is 4, how come the range is 4.

"The greatest difference between any two integers in E is 4" does not mean that if you pick any two integers their difference will be 4. It means that the greatest difference you can get from any pair of integers from E is 4. Since the range is the difference between the largest and the smallest elements of a set, then 4 must be the range of E.

Check this for more on this question: http://gmatclub.com/forum/ps-questions- ... ml#p810657 (or: http://gmatclub.com/forum/e-is-a-collec ... ml#p769204).

Hope it helps.

Bunuel thank you for such a classified question,I could cover SD topic, but unfortuantely I was just wrong about this question.
Why we don't assume negative numbers? such as {-1,-1,1,3} etc...??

{-1, -1, 1, 3} --> range = largest - smallest = 3 - (-1) = 4.
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Joined: 30 Apr 2017
Posts: 87
PS questions about standard deviation. [#permalink]

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14 Oct 2017, 02:35
Question says greatest difference between any two integers in E is 4, how come the range is 4.

"The greatest difference between any two integers in E is 4" does not mean that if you pick any two integers their difference will be 4. It means that the greatest difference you can get from any pair of integers from E is 4. Since the range is the difference between the largest and the smallest elements of a set, then 4 must be the range of E.

{-1, -1, 1, 3} --> range = largest - smallest = 3 - (-1) = 4.

" It means that the greatest difference you can get from any pair of integers from E is 4. "
so what's the problem?? I think I'm confused.
Math Expert
Joined: 02 Sep 2009
Posts: 44320
Re: PS questions about standard deviation. [#permalink]

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14 Oct 2017, 02:39
soodia wrote:
so what's the problem?? I think I'm confused.

What is your question?

P.S. Check here: https://gmatclub.com/forum/ps-questions ... ml#p810657 and here: https://gmatclub.com/forum/e-is-a-colle ... ml#p769204 for more.
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Joined: 30 Apr 2017
Posts: 87
Re: PS questions about standard deviation. [#permalink]

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14 Oct 2017, 03:12
Bunuel wrote:
soodia wrote:
so what's the problem?? I think I'm confused.

What is your question?

P.S. Check here: https://gmatclub.com/forum/ps-questions ... ml#p810657 and here: https://gmatclub.com/forum/e-is-a-colle ... ml#p769204 for more.

The question says: E is a collection of four odd integers and the greatest difference between any two integers in E is 4.
in set {-1,-1,1,3} or {-1,1,1,3},.....
the greatest difference is 4
so why we do not assume these sets to calculate the SD?
Math Expert
Joined: 02 Sep 2009
Posts: 44320
Re: PS questions about standard deviation. [#permalink]

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14 Oct 2017, 03:33
soodia wrote:
Bunuel wrote:
soodia wrote:
so what's the problem?? I think I'm confused.

What is your question?

P.S. Check here: https://gmatclub.com/forum/ps-questions ... ml#p810657 and here: https://gmatclub.com/forum/e-is-a-colle ... ml#p769204 for more.

The question says: E is a collection of four odd integers and the greatest difference between any two integers in E is 4.
in set {-1,-1,1,3} or {-1,1,1,3},.....
the greatest difference is 4
so why we do not assume these sets to calculate the SD?

I believe I already answered this question on previous pages.

{-1,-1,1,3} has the same SD as {1, 1, 3, 5}: by by adding 2 to each term.
{-1,1,1,3} has the same SD as {1, 3, 3, 5}: by by adding 2 to each term.

If we add or subtract a constant to each term in a set SD will not change.
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Joined: 30 Apr 2017
Posts: 87
Re: PS questions about standard deviation. [#permalink]

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14 Oct 2017, 13:50
I believe I already answered this question on previous pages.

{-1,-1,1,3} has the same SD as {1, 1, 3, 5}: by by adding 2 to each term.
{-1,1,1,3} has the same SD as {1, 3, 3, 5}: by by adding 2 to each term.

If we add or subtract a constant to each term in a set SD will not change.[/quote]

I'm sorry for misunderstanding your explanation before
I've just got it
Thank you
Re: PS questions about standard deviation.   [#permalink] 14 Oct 2017, 13:50

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# PS questions about standard deviation.

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