Author 
Message 
TAGS:

Hide Tags

Director
Joined: 03 Sep 2006
Posts: 850

If d is the standard deviation x, y, and z, what is the stan [#permalink]
Show Tags
10 May 2010, 09:37
1
This post received KUDOS
1
This post was BOOKMARKED
Question Stats:
89% (00:12) correct 11% (00:16) wrong based on 246 sessions
HideShow timer Statistics
If d is the standard deviation x, y, and z, what is the standard deviation of x + 5, y + 5, z + 5 ? A. d B. 3d C. 15d D. d + 5 E. d + 15
Official Answer and Stats are available only to registered users. Register/ Login.
Attachments
PS8.PNG [ 8.1 KiB  Viewed 5301 times ]
Last edited by Bunuel on 02 Oct 2013, 03:27, edited 1 time in total.
Renamed the topic, edited the question and added the OA.



Math Expert
Joined: 02 Sep 2009
Posts: 44290

3
This post received KUDOS
Expert's post
4
This post was BOOKMARKED



Director
Joined: 03 Sep 2006
Posts: 850

Bunuel wrote: If d is the standard deviation x, y, and z, what is the standard deviation of x+5, y+5, z+5 A. d B. 3d C. 15d D. d+5 E. d+15 TIP: If we add or subtract a constant to each term in a set:Mean will increase or decrease by the same constant. SD will not change. If we increase or decrease each term in a set by the same percent (multiply by a constant):Mean will increase or decrease by the same percent. SD will increase or decrease by the same percent. So in our case SD won't change as we are adding 5 to each term in a set > SD=d. Answer: A. More about standard deviation: mathstandarddeviation87905.htmldsquestionsaboutstandarddeviation85896.htmlpsquestionsaboutstandarddeviation85897.htmlHope it helps. Thanks very very much! Thanks for the tip



Manager
Joined: 04 May 2010
Posts: 86
WE 1: 2 yrs  Oilfield Service

Re: PS : Stats [#permalink]
Show Tags
10 Jul 2010, 01:28
1
This post received KUDOS
This is conceptual. Standard deviation is a measure of the difference between each value in a set and its mean value.
Now, if x,y and z have a standard deviation of d, this indicates to us that the average deviation of x,y and z from the mean of x,y and z is d.
If we simply shift the entire set of x,y and z along the number line by a quantity of 5, does this alter the amount by which they will vary around their new mean? No, their deviation relative to their mean will not change, as the mean itself has moved correspondingly, maintaining the same differences for x+5, y+5 and z+5. Thus the standard deviation will remain unchanged.
Pick A.



Manager
Joined: 22 Mar 2010
Posts: 56

The tip was handy..Thanks!! OA is A



SVP
Joined: 08 Jul 2010
Posts: 2016
Location: India
GMAT: INSIGHT
WE: Education (Education)

Re: If d is the standard deviation x, y, and z, what is the stan [#permalink]
Show Tags
21 Jul 2015, 10:53
LM wrote: If d is the standard deviation x, y, and z, what is the standard deviation of x + 5, y + 5, z + 5 ?
A. d B. 3d C. 15d D. d + 5 E. d + 15 CONCEPT: Standard Deviation is Defined as Average Deviation of Terms in the set from the Mean value of the set. i.e.
1) It depends on the separation between the successive terms of the set
2) If a Constant Value is Added/Subtracted in every terms of set then the Separation between successive terms does NOT change Hence S.D. remains Constant e.g.{1, 2, 3, 4, 5} will have same standard Deviation as {1+10, 2+10, 3+10, 4+10, 5+10}
3) If a Constant Value is Multiplied in every terms then the Separation between succesive terms gets multiplied by the constant Hence S.D. remains gets multiplied by same Number e.g. {0.7, 1.4, 2.1, 2.8, 3.5} will have Standard Deviation = 0.7* Standard deviation of set {1, 2, 3, 4, 5} When 5 is added in each term of set {x, y, z} then the new set {x+5, y+5, z+5} will remain same as the previous standard deviation i.e. d Answer: Option A
_________________
Prosper!!! GMATinsight Bhoopendra Singh and Dr.Sushma Jha email: info@GMATinsight.com I Call us : +919999687183 / 9891333772 Online OneonOne Skype based classes and Classroom Coaching in South and West Delhi http://www.GMATinsight.com/testimonials.html
22 ONLINE FREE (FULL LENGTH) GMAT CAT (PRACTICE TESTS) LINK COLLECTION



Target Test Prep Representative
Status: Founder & CEO
Affiliations: Target Test Prep
Joined: 14 Oct 2015
Posts: 2293
Location: United States (CA)

Re: If d is the standard deviation x, y, and z, what is the stan [#permalink]
Show Tags
24 Sep 2016, 07:54
LM wrote: If d is the standard deviation x, y, and z, what is the standard deviation of x + 5, y + 5, z + 5 ?
A. d B. 3d C. 15d D. d + 5 E. d + 15 In a data set, if every number is increased (or decreased) by the same amount, the standard deviation of the data set will not be affected. That is, the new standard deviation is still equal to the original standard deviation. Here we see that each data value is increased by the same amount (5 in this case); therefore, the standard deviation will still be d. Answer: A
_________________
Scott WoodburyStewart
Founder and CEO
GMAT Quant SelfStudy Course
500+ lessons 3000+ practice problems 800+ HD solutions



EMPOWERgmat Instructor
Status: GMAT Assassin/CoFounder
Affiliations: EMPOWERgmat
Joined: 19 Dec 2014
Posts: 11255
Location: United States (CA)
GRE 1: 340 Q170 V170

Re: If d is the standard deviation x, y, and z, what is the stan [#permalink]
Show Tags
03 Mar 2018, 15:45
Hi All, In real basic terms, Standard Deviation is a measure of how "spread out" a group of numbers is. Numbers that are "close together" will create a small Standard Deviation, while numbers that are really "spread out" will create a large Standard Deviation. Here, we have 3 values: X, Y and Z. We're told that they have a Standard Deviation of D. To help you visualize what's going on here, let's TEST VALUES… X = 1 Y = 2 Z = 3 Standard Deviation = D (don't worry about calculating it, the GMAT will NEVER ask you to calculate a Standard Deviation) Notice the "spread" of the above numbers; we'll come back to this in a moment. The question then asks us to think about X+5, Y+5 and Z+5. Using the values from above, we would have…. 1+5 = 6 2+5 = 7 3+5 = 8 Now, notice how these values have the exact SAME SPREAD as the initial set of numbers? This group of numbers has the SAME STANDARD DEVIATION as the original set of numbers. Thus, the Stand Deviation is still D. Final Answer: GMAT assassins aren't born, they're made, Rich
_________________
760+: Learn What GMAT Assassins Do to Score at the Highest Levels Contact Rich at: Rich.C@empowergmat.com
Rich Cohen
CoFounder & GMAT Assassin
Special Offer: Save $75 + GMAT Club Tests Free
Official GMAT Exam Packs + 70 Pt. Improvement Guarantee www.empowergmat.com/
***********************Select EMPOWERgmat Courses now include ALL 6 Official GMAC CATs!***********************




Re: If d is the standard deviation x, y, and z, what is the stan
[#permalink]
03 Mar 2018, 15:45






