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String of bulbs

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String of bulbs [#permalink] New post 04 Jul 2009, 21:40
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A string of 10 lightbulbs is wired in such a way that if
any individual lightbulb fails, the entire string fails. If for
each individual lightbulb the probability of failing during
time period T id 0.06, what is the probability that the
string of lightbulbs will fail during time period T?
A.0.06
B.(0.06)^10
C.1-(0.06)^10
D.(0.94)^10
E.1-(0.94)^10
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Re: String of bulbs [#permalink] New post 05 Jul 2009, 01:47
Economist wrote:
A string of 10 lightbulbs is wired in such a way that if
any individual lightbulb fails, the entire string fails. If for
each individual lightbulb the probability of failing during
time period T id 0.06, what is the probability that the
string of lightbulbs will fail during time period T?
A.0.06
B.(0.06)^10
C.1-(0.06)^10
D.(0.94)^10
E.1-(0.94)^10



A

OA please.

What if the questions was the probability of failing during the time period T is 0.06 for 9 of the lightbulbs and 0.05 for the 10th lightbulb what is the probablility that the string will fail during time period T
=
(0.06(9) + 0.05)/10

Please comment.
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Re: String of bulbs [#permalink] New post 05 Jul 2009, 07:47
Lets get some posts before I post OA.
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Re: String of bulbs [#permalink] New post 05 Jul 2009, 08:47
E

1) the probability of not failing for one bulb: 1 - 0.06 =0.94
2) the probability of not failing for 10 bulbs: 0.94^10
3) the probability of failing for the string of 10 bulbs): 1 - 0.94^10
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Re: String of bulbs [#permalink] New post 05 Jul 2009, 09:40
nightwing79 wrote:
Economist wrote:
A string of 10 lightbulbs is wired in such a way that if
any individual lightbulb fails, the entire string fails. If for
each individual lightbulb the probability of failing during
time period T id 0.06, what is the probability that the
string of lightbulbs will fail during time period T?
A.0.06
B.(0.06)^10
C.1-(0.06)^10
D.(0.94)^10
E.1-(0.94)^10



A

OA please.


walker is right.

E it should be.
failing during the time period T is 0.06 for 9 of the lightbulbs and 0.05 for the 10th lightbulb what is the probablility that the string will fail during time period T
=
(0.06(9) + 0.05)/10

Please comment.



walker is right.

E it should be. silly silly.
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Re: String of bulbs [#permalink] New post 05 Jul 2009, 11:45
nightwing79 wrote:
walker is right.

E it should be. silly silly.


silly mistakes is a main reason why I got 50 instead of 51 in Quant.....tricky GMAT
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Re: String of bulbs   [#permalink] 05 Jul 2009, 11:45
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