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# a fair 2-sided coin is flipped 6 times. what is the

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CEO
Joined: 21 Jan 2007
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a fair 2-sided coin is flipped 6 times. what is the [#permalink]  18 May 2007, 20:56
a fair 2-sided coin is flipped 6 times. what is the probability that the tails will be the result at least twice, but not more than 5 times?

once again, Princeton Review uses plugging in. How can i solve this algebraically?
Current Student
Joined: 22 Apr 2007
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6 flips -> total combinations = 2^6 = 64

P(tails 0 times) = 1/64

P(tails only once) = 6/64

P(tails all 6 times) = 1/64

So, P(Together) = 8/64

So, P(at least twice and no more than 5) = 1 - 8/64 = 56/64 = 7/8

Director
Joined: 26 Feb 2006
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Re: PR Probability Bin 4 [#permalink]  18 May 2007, 21:14
1
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bmwhype2 wrote:
a fair 2-sided coin is flipped 6 times. what is the probability that the tails will be the result at least twice, but not more than 5 times?

once again, Princeton Review uses plugging in. How can i solve this algebraically?

Tail = 6c2 + 6c3 + 6c4 + 6c5 = 56
p = 56/64 = 7/8
SVP
Joined: 28 Dec 2005
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Re: PR Probability Bin 4 [#permalink]  15 Feb 2008, 05:11
isnt this a question that you apply binomial theorem to ?

so we are looking for probability of 2/3/4 heads out of 6 flips

Re: PR Probability Bin 4   [#permalink] 15 Feb 2008, 05:11
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