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The lifetime of all the batteries produced by a certain comp

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The lifetime of all the batteries produced by a certain comp [#permalink] New post 21 Sep 2010, 20:34
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The lifetime of all the batteries produced by a certain company in a year have a distribution that is symmetric about the mean m. If the distribution has a standard deviation of d, what percent of the distribution is greater than m+d?

(1) 68 percent of the distribution lies in the interval from m-d to m+d, inclusive
(2) 16 percent of the distribution is less than m-d

Can sum1 explain the concept behind this...Looking at the answer I have come up with my own assumptions...
[Reveal] Spoiler: OA

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Last edited by Bunuel on 02 Feb 2012, 09:48, edited 1 time in total.
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Re: SD symmetric about the mean [#permalink] New post 21 Sep 2010, 20:59
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The lifetime of all the batteries produced by a certain company in a year have a distribution that is symmetric about the mean m. If the distribution has a standard deviation of d, what percent of the distribution is greater than m+d?

Symmetric about the mean means that the shape of the distribution on the right and left side of the curve are mirror-images of each other.

(1) 68% of the distribution lies in the interval from m-d to m+d, inclusive --> 100%-68%=32% is less than m-d and more than m+d. As distribution is symmetric about the mean then exactly half of 32%, or 16%, would be more than m+d. Sufficient.

(2) 16% of the distribution is less than m-d --> again, as distribution is symmetric about the mean then exactly 16%, will be more than m+d. Sufficient.

Answer: D.

Hope it helps.
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Re: SD symmetric about the mean [#permalink] New post 22 Sep 2010, 15:34
Thank you. I drew a diagram with normal distribution and came up with this assumptions...But now I am happy looking at ur explanations that my assumptions are true.
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Re: SD symmetric about the mean [#permalink] New post 22 Sep 2010, 15:42
Nice question. Key word was symmetric to clearly mark the answer as D
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Re: SD symmetric about the mean [#permalink] New post 15 Mar 2011, 23:31
Bunuel wrote:
The lifetime of all the batteries produced by certain companies have a distribution which is symmetric about mean m. If the distribution has a standard deviation of d , what percentage of distribution is greater than m+d?

Symmetric about the mean means that the shape of the distribution on the right and left side of the curve are mirror-images of each other.

(1) 68% of the distribution lies in the interval from m-d to m+d, inclusive --> 100%-68%=32% is less than m-d and more than m+d. As distribution is symmetric about the mean then exactly half of 32%, or 16%, would be more than m+d. Sufficient.

(2) 16% of the distribution is less than m-d --> again, as distribution is symmetric about the mean then exactly 16%, will be more than m+d. Sufficient.

Answer: D.

Hope it helps.

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Re: SD symmetric about the mean [#permalink] New post 16 Mar 2011, 21:49
This is all related to the concepts related to bell curve and normal distribution.

Bunuel/Ian, are these concepts tested in GMAT ?
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Re: SD symmetric about the mean [#permalink] New post 02 Feb 2012, 09:09
@ ghosh

bell curve is an important topic and often questions crop up.
i got one such in my gmat, though it was east, but the qs stem is verbose and one has to make out that its a qs on bell curve.
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Re: The lifetime of all the batteries produced by a certain comp [#permalink] New post 24 May 2013, 03:20
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Re: SD symmetric about the mean [#permalink] New post 02 Jul 2013, 05:57
Bunuel wrote:
The lifetime of all the batteries produced by a certain company in a year have a distribution that is symmetric about the mean m. If the distribution has a standard deviation of d, what percent of the distribution is greater than m+d?

Symmetric about the mean means that the shape of the distribution on the right and left side of the curve are mirror-images of each other.

(1) 68% of the distribution lies in the interval from m-d to m+d, inclusive --> 100%-68%=32% is less than m-d and more than m+d. As distribution is symmetric about the mean then exactly half of 32%, or 16%, would be more than m+d. Sufficient.

(2) 16% of the distribution is less than m-d --> again, as distribution is symmetric about the mean then exactly 16%, will be more than m+d. Sufficient.

Answer: D.

Hope it helps.


How valuable is the portion in red if you don't read the question carefully would have marked C instead of D!
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Re: SD symmetric about the mean   [#permalink] 02 Jul 2013, 05:57
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