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PS questions about standard deviation.

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Re: PS questions about standard deviation. [#permalink]

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New post 13 Oct 2017, 08:37
Bunuel would you please provide the OA for the given problems

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Re: PS questions about standard deviation. [#permalink]

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New post 13 Oct 2017, 08:43

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Re: PS questions about standard deviation. [#permalink]

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New post 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...??

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Re: PS questions about standard deviation. [#permalink]

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New post 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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Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


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PS questions about standard deviation. [#permalink]

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New post 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.

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Re: PS questions about standard deviation. [#permalink]

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New post 14 Oct 2017, 02:39

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Re: PS questions about standard deviation. [#permalink]

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New post 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?

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Re: PS questions about standard deviation. [#permalink]

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New post 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.
_________________

New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.

Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


What are GMAT Club Tests?
Extra-hard Quant Tests with Brilliant Analytics

Kudos [?]: 132991 [0], given: 12402

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Re: PS questions about standard deviation. [#permalink]

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New post 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 :)

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Re: PS questions about standard deviation.   [#permalink] 14 Oct 2017, 13:50

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