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The lifetimes of all the batteries produced by a certain

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28 Sep 2006, 14:10
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The lifetimes 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

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28 Sep 2006, 14:30
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The lifetimes 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

from one

32 percent of the distribution lies outside the interval m-d to m+d,

thus 32/2 = 16 percent is greater than m+d...suff

from two

if 16 percent of the distribution is less than m-d and since it is a normal (symetric) ditribution thus 16 percent is greater than m+d.suff

Last edited by yezz on 28 Sep 2006, 14:57, edited 1 time in total.
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28 Sep 2006, 14:55
I thot it was C too but GMATPREP slapped me and was like NOOOOO its not C
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29 Sep 2006, 00:40
Some knowledge transfer from yezz again,

Thaks a lot yezz

Keep rocking.............
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Last edited by cicerone on 25 Sep 2008, 00:13, edited 1 time in total.
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29 Sep 2006, 06:24
Yep, the key point here is "symmetric about the mean" = normal distribution.

(D)
29 Sep 2006, 06:24
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