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Set A consists of all even integers between 2 and 100

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Set A consists of all even integers between 2 and 100 [#permalink] New post 14 Mar 2011, 08:20
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Set A consists of all even integers between 2 and 100, inclusive. Set X is derived by reducing each term in set A by 50, set Y is derived by multiplying each term in set A by 1.5, and set Z is derived by dividing each term in set A by -4. Which of the following represents the ranking of the three sets in descending order of standard deviation?

(A) X, Y, Z
(B) X, Z, Y
(C) Y, Z, X
(D) Y, X, Z
(E) Z, Y, X
[Reveal] Spoiler: OA

Last edited by Bunuel on 17 Jul 2012, 02:34, edited 1 time in total.
Edited the OA.
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Re: std deviation [#permalink] New post 14 Mar 2011, 09:12
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punyadeep wrote:
Set A consists of all even integers between 2 and 100, inclusive. Set X is derived by reducing each term in set A by 50, set Y is derived by multiplying each term in set A by 1.5, and set Z is derived by dividing each term in set A by -4. Which of the following represents the ranking of the three sets in descending order of standard deviation?
(A) X, Y, Z
(B) X, Z, Y
(C) Y, Z, X
(D) Y, X, Z
(E) Z, Y, X

pls explain the concept too....?? how do we find the spread frm mean when there r many terms involved..??


Set A - {2, 4, ..., 100};
Set X - {-48, -46, ..., 50};
Set Y - {3, 6, ..., 150};
Set Z - {-2/4, -4/4, ..., -100/4} = {-1/2, -1, -3/2, ..., -25}.

If we add or subtract a constant to each term in a set the SD will not change, so sets A and X will have the same SD.

If we increase or decrease each term in a set by the same percent (multiply by a constant) the SD will increase or decrease by the same percent, so set Y will have 1.5 times greater SD than set A and set Z will have 4 times less SD than set A (note SD can not be negative so SD of Z wil be SD of A divided by 4 not by -4).

So, the ranking of SD's in descending order is: Y, A=X, Z.

Answer: D.

Or the sane way as here: standard-deviation-110874.html#p890965

The standard deviation of a set shows how much variation there is from the mean, how widespread a given set is. So, a low standard deviation indicates that the data points tend to be very close to the mean, whereas high standard deviation indicates that the data are spread out over a large range of values.

You can see that set Y is most widespread and set Z is least widespread, so the correct answer is: Y, A=X, Z.

Answer: D.

For more on SD check:
math-standard-deviation-87905.html
ds-questions-about-standard-deviation-85896.html
ps-questions-about-standard-deviation-85897.html
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Re: std deviation [#permalink] New post 14 Mar 2011, 18:28
The answer is D, I think the OA is wrongly posted as E.
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Re: std deviation [#permalink] New post 17 Apr 2011, 12:51
it is D. See Bunuel's explaination.
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Re: std deviation [#permalink] New post 17 Apr 2011, 18:06
Answer is D - Y,X,Z

For X - SD remains unchanged

For Y - SD is multiplied by 1.5

For Z - SD is divided by -4

OA given is wrong.
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Re: Set A consists of all even integers between 2 and 100 [#permalink] New post 12 Jul 2013, 01:35
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Re: Set A consists of all even integers between 2 and 100 [#permalink] New post 09 Aug 2014, 20:00
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Re: Set A consists of all even integers between 2 and 100 [#permalink] New post 20 Aug 2014, 15:18
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Hi Bunnel,

Here in the question the arrangement asked is in descending order then why answer is D.

D option's arrangement is in ascending order isn't it.
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Re: Set A consists of all even integers between 2 and 100 [#permalink] New post 21 Aug 2014, 03:00
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taleesh wrote:
Hi Bunnel,

Here in the question the arrangement asked is in descending order then why answer is D.

D option's arrangement is in ascending order isn't it.


Y has the greatest SD, then comes X followed by Z, which has the least SD. So, Y, X, Z is in descending order.
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PLEASE READ AND FOLLOW: 11 Rules for Posting!!!

RESOURCES: [GMAT MATH BOOK]; 1. Triangles; 2. Polygons; 3. Coordinate Geometry; 4. Factorials; 5. Circles; 6. Number Theory; 7. Remainders; 8. Overlapping Sets; 9. PDF of Math Book; 10. Remainders; 11. GMAT Prep Software Analysis NEW!!!; 12. SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) NEW!!!; 12. Tricky questions from previous years. NEW!!!;

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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Re: Set A consists of all even integers between 2 and 100 [#permalink] New post 21 Aug 2014, 08:17
Hi Bunnel,

Thanks for the reply, i realized now it should be greater to smaller. Got confused, now it is clear.
Re: Set A consists of all even integers between 2 and 100   [#permalink] 21 Aug 2014, 08:17
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