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Mean and standard deviation

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by deepak123gmat » Fri Oct 08, 2010 6:06 am
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 percentage of the distribution is greater than m+d?
1) 68% of the distribution lies in the interval from m-d to m+d inclusive.
2) 16% of the distribution is less than m-d.
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Source: — Data Sufficiency |
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by kmittal82 » Fri Oct 08, 2010 6:31 am
Stmt1)

68% lies between m-d and m+d, which means the other 32% lies outside that area.

since the disutrubution is symmetric about the mean, this 32% will be equally divided between less than m-d and more than m+d

thus, % more than m+d = 32/2 = 16%

Sufficient

Stmt2)

If 16% is less than m-d, then 16% is also greater than m+d, since the distribution is symmetric.

sufficient

IMO, (D). OA please?
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by ankurmit » Fri Oct 08, 2010 9:41 am
Yup Kmittal82 you are right.
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by deepak123gmat » Fri Oct 08, 2010 11:43 am
yep. OA is D
thanks folks
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