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In which range does deviation lie

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Re: In which range does deviation lie

by real2008 » Mon Aug 24, 2009 9:21 am
goelmohit2002 wrote:In which range does deviation of 11, 10, 10, 10, 12 and 12 lie.

[spoiler]OA = between 0 and 3. Can someone please tell why not between 0 and 1....if Standard deviation <= Range/2[/spoiler]
can u pl post the full question? pl mention the source also.
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by goelmohit2002 » Mon Aug 24, 2009 9:43 am
This is complete question....

Source = one of my friends gave me this....he was given the same as part of his class assignment in GMAT coaching.
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by real2008 » Mon Aug 24, 2009 10:01 am
i find SD to be 0.897 and range 2.

It seems to me 'range' as mentioned in the qn. is not the range as used in statistics but range (say a<SD<b) in which the SD lies.

Now the SD, as calculated, lies between 0 and 3 and probably this choice best describes among the other available choices (I am not finding the choices in the post).


Please correct me if I misunderstand.
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by PussInBoots » Mon Aug 24, 2009 3:46 pm
I believe deviation is fancy word for difference. The actual range of deviation is 0 (10 - 10) to 2 (12-10).
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by Waqas_Jameel » Mon Sep 16, 2013 6:46 am
goelmohit2002 wrote:In which range does deviation of 11, 10, 10, 10, 12 and 12 lie.

[spoiler]OA = between 0 and 3. Can someone please tell why not between 0 and 1....if Standard deviation <= Range/2[/spoiler]

I did like an explanation from some of the GMAT titans here
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by Brent@GMATPrepNow » Mon Sep 16, 2013 7:29 am
In which range does deviation of 11, 10, 10, 10, 12 and 12 lie.
First of all, since this question does not have 5 answer choices, it's not a true GMAT question.

It may be possible that there's a rule that says: Standard Deviation < Range/2, I'm not sure.
However, we can be certain that Standard Deviation < Range, and that's all we need here.

Since the range = 2, we can be certain that the Standard Deviation < 2, so the standard deviation must lie between 0 and 3

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by Waqas_Jameel » Mon Sep 16, 2013 7:33 am
Hmm.. can be .. anyways .. thanks a ton for the fast response
Brent@GMATPrepNow wrote:
In which range does deviation of 11, 10, 10, 10, 12 and 12 lie.
First of all, since this question does not have 5 answer choices, it's not a true GMAT question.

It may be possible that there's a rule that says: Standard Deviation < Range/2, I'm not sure.
However, we can be certain that Standard Deviation < Range, and that's all we need here.

Since the range = 2, we can be certain that the Standard Deviation < 2, so the standard deviation must lie between 0 and 3

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by [email protected] » Mon Sep 16, 2013 3:04 pm
Hi All,

The GMAT will never ask you to calculate the Standard Deviation of a group of numbers. You MIGHT be asked if a Standard Deviation gets larger or smaller when you change the group (by adding or removing elements), but you'll never be asked to do the math. In that situation, it's about understanding what SD is and how it changes.

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by Brent@GMATPrepNow » Mon Sep 16, 2013 3:16 pm
I wholeheartedly agree with Rich.
To get an idea of the types of Standard Deviation questions one might encounter on the GMAT, check out these questions:
- https://www.beatthegmat.com/tricky-ds-sd ... 68907.html
- https://www.beatthegmat.com/number-quest ... 68283.html
- https://www.beatthegmat.com/sd-t247883.html
- https://www.beatthegmat.com/call-for-hel ... 53493.html
- https://www.beatthegmat.com/if-m-is-a-ne ... 48841.html

Even more here: https://www.beatthegmat.com/forums/tags/ ... -deviation

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by ganeshrkamath » Mon Sep 16, 2013 8:31 pm
goelmohit2002 wrote:In which range does deviation of 11, 10, 10, 10, 12 and 12 lie.

[spoiler]OA = between 0 and 3. Can someone please tell why not between 0 and 1....if Standard deviation <= Range/2[/spoiler]
This looks more like a GRE problem than a GMAT problem.

Let me take you through the calculations involved anyway:
average = (10+10+10+11+12+12)/6 = 65/6
std. dev. = sqrt(variance)
= sqrt((3*(5/6)^2 + 1/36 + 2*(7/6)^2)/6)
= sqrt((75/36 + 1/36 + 98/36)/6)
= sqrt((174/36)/6)
= sqrt(174/216)
= sqrt(29/36)
The answer indeed lies between 0 and 3.

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