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Is the deviation of x, y, and z equal to the deviation of [#permalink]
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06 May 2006, 05:07
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Is the deviation of x, y, and z equal to the deviation of 10, 15, 20?
1) xy=5
2) xz=10



VP
Joined: 29 Dec 2005
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Re: Deviation of 10, 15, 20 [#permalink]
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10 May 2006, 22:06
getzgetzu wrote: Is the deviation of x, y, and z equal to the deviation of 10, 15, 20?
1) xy=5 2) xz=10
E... we donot know the value of x????



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Joined: 13 Nov 2003
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I am not pretty sure but i think it is C)
A and B by itself are both insufficient. The third value is missing.
From both A) X=5+Y and B) X=10+Z and 5+Y=10+Z then Y=5+Z and from B) X=10+Z, then the values are Z, 5+Z, 10+Z and the deviation is 5 as it is in the stem.



Director
Joined: 24 Oct 2005
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SD of 5, 10, 15 is 5.
Statement 1 says , x  y = 5.
But we dont know about z to decide.
Statement 2 says xz = 10.
But we dont know position of y.
But combing these two,
we know that the numbers come in the order x y z with a difference of 5 each. SD = 5 . [We do not need value of y. We just want to know the difference between other nos and y. ]
Hence C.



Intern
Joined: 23 Feb 2006
Posts: 39

Agree with BG.
Think it's C.
Try to pick up numbers
let's say y=15 then x=5+y=15+5=20 and z=x10=10. So we have 10 15 20 and deviation is the same...moreover in general case as BG has shown we have numbers like Z,Z+5,Z+10 and we know that D(x)=sqrt((Xavg(X,Y,Z))^2+(Yavg(X,Y,Z))^2+(Zavg(X,Y,Z))^2)/(n1) so we can see that the difference in bracket would be always the same if the number follow the pattern Z,Z+5,Z+10....



VP
Joined: 06 Jun 2004
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BG wrote: I am not pretty sure but i think it is C) A and B by itself are both insufficient. The third value is missing. From both A) X=5+Y and B) X=10+Z and 5+Y=10+Z then Y=5+Z and from B) X=10+Z, then the values are Z, 5+Z, 10+Z and the deviation is 5 as it is in the stem.
Great explanation! I guess I fell for the trap.
OA pls?
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VP
Joined: 29 Dec 2005
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TeHCM wrote: BG wrote: I am not pretty sure but i think it is C) A and B by itself are both insufficient. The third value is missing. From both A) X=5+Y and B) X=10+Z and 5+Y=10+Z then Y=5+Z and from B) X=10+Z, then the values are Z, 5+Z, 10+Z and the deviation is 5 as it is in the stem. Great explanation! I guess I fell for the trap. OA pls?
sorry guys i forget to apply range concept. if the range of a given number of observations is equal with the same no of observations, the SDs of these observations are equal and its toooooo late to apply this concept.
i misjudged that SD is higher with higher values....










