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String of bulbs

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Director
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Joined: 01 Apr 2008
Posts: 904
Schools: IIM Lucknow (IPMX) - Class of 2014
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Kudos [?]: 345 [0], given: 18

String of bulbs [#permalink] New post 04 Jul 2009, 20:40
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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
Manager
Manager
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Joined: 11 Apr 2009
Posts: 212
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Kudos [?]: 83 [0], given: 4

Re: String of bulbs [#permalink] New post 05 Jul 2009, 00:47
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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Director
Director
User avatar
Joined: 01 Apr 2008
Posts: 904
Schools: IIM Lucknow (IPMX) - Class of 2014
Followers: 18

Kudos [?]: 345 [0], given: 18

Re: String of bulbs [#permalink] New post 05 Jul 2009, 06:47
Lets get some posts before I post OA.
Expert Post
CEO
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Joined: 17 Nov 2007
Posts: 3574
Concentration: Entrepreneurship, Other
Schools: Chicago (Booth) - Class of 2011
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Re: String of bulbs [#permalink] New post 05 Jul 2009, 07:47
Expert's post
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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Manager
Manager
User avatar
Joined: 11 Apr 2009
Posts: 212
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Kudos [?]: 83 [0], given: 4

Re: String of bulbs [#permalink] New post 05 Jul 2009, 08:40
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.
_________________

-talent is the desire to practice-

Expert Post
CEO
CEO
User avatar
Joined: 17 Nov 2007
Posts: 3574
Concentration: Entrepreneurship, Other
Schools: Chicago (Booth) - Class of 2011
GMAT 1: 750 Q50 V40
Followers: 424

Kudos [?]: 2302 [0], given: 359

GMAT ToolKit User Premium Member
Re: String of bulbs [#permalink] New post 05 Jul 2009, 10:45
Expert's post
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, 10:45
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String of bulbs

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