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The lifetimes of all batteries produced by XYZ in a year

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The lifetimes of all batteries produced by XYZ in a year [#permalink] New post 10 Aug 2008, 08:54
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The lifetimes of all batteries produced by XYZ in a year have a distribution that is symmetric about their mean m. If the distribution has a standard deviation of d. What percent of the distribution is greater than m+d ?

(1) 68% of the distribution lies between interval m-d and m+d inclusive
(2) 16% of the distribution is less than m-d

Can someone explain this please?
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Re: GMATPREP DS- Can someone explain? [#permalink] New post 10 Aug 2008, 09:00
aaron22197 wrote:
The lifetimes of all batteries produced by XYZ in a year have a distribution that is symmetric about their mean m. If the distribution has a standard deviation of d. What percent of the distribution is greater than m+d ?

(1) 68% of the distribution lies between interval m-d and m+d inclusive
(2) 16% of the distribution is less than m-d

Can someone explain this please?


C)

Distribution greater than m + d = 100 - 68 - 16 = 24
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Re: GMATPREP DS- Can someone explain? [#permalink] New post 10 Aug 2008, 09:21
aaron22197 wrote:
that's not the OA.


I missed the word symmetric graph. Its like a inverted parabola around mean.

If you consider symmetry then OA will be D)

However I doubt you can have distribution in GMAT.
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Re: GMATPREP DS- Can someone explain? [#permalink] New post 10 Aug 2008, 09:45
nmohindru wrote:
aaron22197 wrote:
that's not the OA.


I missed the word symmetric graph. Its like a inverted parabola around mean.

If you consider symmetry then OA will be D)

However I doubt you can have distribution in GMAT.


This is a GMATPREP question. Can you please explain how you arrived at the solution? I know the OA. I need help understanding the question.
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Re: GMATPREP DS- Can someone explain? [#permalink] New post 10 Aug 2008, 09:53
key here is "distribution is symmetric"

statement 1 : 68% is between m-d and m+d .... greater than m+d = (100-68)/2.... suff...

statement 2 : if 16% is less than m-d .... same should be greater than m+d ... suff ....
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Re: GMATPREP DS- Can someone explain? [#permalink] New post 10 Aug 2008, 10:04
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aaron22197 wrote:
nmohindru wrote:
aaron22197 wrote:
that's not the OA.


I missed the word symmetric graph. Its like a inverted parabola around mean.

If you consider symmetry then OA will be D)

However I doubt you can have distribution in GMAT.


This is a GMATPREP question. Can you please explain how you arrived at the solution? I know the OA. I need help understanding the question.


I am attaching a picture taken from wikipedia to try to illustrate. Pictorial works better for me to understand.
As one can see, if the distribution is symmetric, it means that half will be above the mean and half below.

For the given proble, it means that, 32% is distributed above and below m+d and m-d respectively. i.e. 16% is greater than m+d
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Standard_deviation_illustration.gif
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Re: GMATPREP DS- Can someone explain?   [#permalink] 10 Aug 2008, 10:04
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