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# The lifetimes of all the batteries produced by a certain

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Senior Manager
Joined: 05 Jun 2005
Posts: 455
Followers: 1

Kudos [?]: 22 [0], given: 0

The lifetimes of all the batteries produced by a certain [#permalink]  28 Sep 2006, 14:10
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0% (00:00) correct 0% (00:00) wrong based on 0 sessions
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

SVP
Joined: 05 Jul 2006
Posts: 1519
Followers: 5

Kudos [?]: 115 [1] , given: 39

[#permalink]  28 Sep 2006, 14:30
1
KUDOS
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

My answer is thus D

Last edited by yezz on 28 Sep 2006, 14:57, edited 1 time in total.
Senior Manager
Joined: 05 Jun 2005
Posts: 455
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Kudos [?]: 22 [0], given: 0

GMATPREP-DS-Batteries [#permalink]  28 Sep 2006, 14:55
I thot it was C too but GMATPREP slapped me and was like NOOOOO its not C
Senior Manager
Joined: 28 Aug 2006
Posts: 302
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[#permalink]  29 Sep 2006, 00:40
Some knowledge transfer from yezz again,

Thaks a lot yezz

Keep rocking.............
_________________

Last edited by cicerone on 25 Sep 2008, 00:13, edited 1 time in total.
Current Student
Joined: 29 Jan 2005
Posts: 5244
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Kudos [?]: 179 [0], given: 0

[#permalink]  29 Sep 2006, 06:24
Yep, the key point here is "symmetric about the mean" = normal distribution.

(D)
[#permalink] 29 Sep 2006, 06:24
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# The lifetimes of all the batteries produced by a certain

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