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# A contest will consist of N questions, each of which is to

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Senior Manager
Joined: 05 Oct 2008
Posts: 258
A contest will consist of N questions, each of which is to  [#permalink]

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08 Nov 2008, 04:33
A contest will consist of N questions, each of which is to be answered either True or False. Anyone who answers all N questions correctly will be the winner. What is the least value of N for which the probability is less than 1/1000 that a persoan who randomly guesses the answer to each question will be a winner.

5
10
50
100
1000

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Intern
Joined: 07 Nov 2008
Posts: 29

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08 Nov 2008, 05:18
1
if there is only 1 question in the contest, the probability is 1/2
so the probability of N questions is (1/2)^N

if the peobability is less than 1/1000, (1/2)^N < 1/1000, ---> the minimum of N is 10, (2^10 = 1024)
VP
Joined: 05 Jul 2008
Posts: 1329

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08 Nov 2008, 12:03
1
Agree its B N= 10 Q means the probability of getting all Q's correct is 1/1024 and it is less than 1/1000

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Re: Probability &nbs [#permalink] 08 Nov 2008, 12:03
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# A contest will consist of N questions, each of which is to

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