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# If d is the standard deviation x, y, and z, what is the stan

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Senior Manager
Joined: 05 Aug 2005
Posts: 399
If d is the standard deviation x, y, and z, what is the stan  [#permalink]

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Updated on: 02 Oct 2013, 03:28
3
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Difficulty:

5% (low)

Question Stats:

80% (00:07) correct 20% (00:10) wrong based on 407 sessions

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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

OPEN DISCUSSION OF THIS QUESTION IS HERE: if-d-is-the-standard-deviation-x-y-and-z-what-is-the-stan-93979.html

Originally posted by gmacvik on 07 Oct 2006, 12:52.
Last edited by Bunuel on 02 Oct 2013, 03:28, edited 1 time in total.
Edited the question and added the OA.
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Joined: 05 Jul 2006
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07 Oct 2006, 14:59
2
If d is the standard deviation x,y,and z, what is the standard deviation of x+5,y+5,z+5

1) d
2) 3d
3) 15d
4) d+5
5) d+15

mean = x+y+z+15 / 3 = x+y+7/3+5

varinace = (mean - each value )^2

mean increased by 5 and each value increased with same value

thus variance remains as is and thus sd is the same
Manager
Joined: 12 Jul 2006
Posts: 114

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07 Oct 2006, 15:57
Right - adding or subtracting the same number to all numbers in a set does not change the SD. Multiplying or dividing the same number to all numbers in a set does change the SD.
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I think I can. I think I can. I think I can.

Senior Manager
Joined: 01 Oct 2006
Posts: 486

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08 Oct 2006, 03:15
17
22

1) If you a add a constant to all terms of a set SD remains the same
2) If you multiply all terms by a constant k new SD k times old SD
3) To determine whether SD for set A is greatero kno SD for a set B we need to the actual terms. Any information abt mean median or range or their combination is not sufficient.
4) basically SD is tedency to deviate from mean. More data deviates more is sd and less the data smaller is SD.

HTH
Yogesh
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Joined: 23 Jun 2005
Posts: 815
GMAT 1: 740 Q48 V42

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08 Oct 2006, 05:11
D)d+5

Pure POE and guess work - so, if not D, then it's A.
Senior Manager
Joined: 28 Aug 2006
Posts: 302

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08 Oct 2006, 06:07
It is A.

Hey Yogesh, that's what the aspirants here need................
Keep rocking.........
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Posts: 47981
Re: If d is the standard deviation x, y, and z, what is the stan  [#permalink]

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02 Oct 2013, 03:30
5
12
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.

math-standard-deviation-87905.html

OPEN DISCUSSION OF THIS QUESTION IS HERE: if-d-is-the-standard-deviation-x-y-and-z-what-is-the-stan-93979.html
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Posts: 7756
Re: If d is the standard deviation x, y, and z, what is the stan  [#permalink]

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30 Jul 2018, 14:04
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: If d is the standard deviation x, y, and z, what is the stan &nbs [#permalink] 30 Jul 2018, 14:04
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