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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]

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14 Mar 2011, 09:20
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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, 03:34, edited 1 time in total.
Edited the OA.
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14 Mar 2011, 10:12
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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

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.

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.

For more on SD check:
math-standard-deviation-87905.html
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14 Mar 2011, 19:28
The answer is D, I think the OA is wrongly posted as E.
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17 Apr 2011, 13:51
it is D. See Bunuel's explaination.
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17 Apr 2011, 19:06

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]

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12 Jul 2013, 02:35
Bumping for review and further discussion.
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Re: Set A consists of all even integers between 2 and 100 [#permalink]

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09 Aug 2014, 21:00
Hello from the GMAT Club BumpBot!

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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Re: Set A consists of all even integers between 2 and 100 [#permalink]

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20 Aug 2014, 16:18
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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]

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21 Aug 2014, 04:00
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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Re: Set A consists of all even integers between 2 and 100 [#permalink]

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21 Aug 2014, 09:17
Hi Bunnel,

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

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27 Aug 2015, 11:53
Hello from the GMAT Club BumpBot!

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Re: Set A consists of all even integers between 2 and 100 [#permalink]

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01 Dec 2016, 15:55
Hello from the GMAT Club BumpBot!

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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Re: Set A consists of all even integers between 2 and 100 [#permalink]

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02 Dec 2016, 05:02
So division (as in dividing every term in the set by the same number) makes the SD smaller, correct?

I understand the problem and what concepts apply but was lost when it came to division and SD.
Re: Set A consists of all even integers between 2 and 100   [#permalink] 02 Dec 2016, 05:02
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