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If a coin has a probability of landing heads up or tails

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VP
Joined: 06 Jun 2004
Posts: 1059
Location: CA
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If a coin has a probability of landing heads up or tails [#permalink]  26 Dec 2005, 18:06
If a coin has a probability of landing heads up or tails each time it is flipped, what is the probability that the coin will land heads up exactly twice in 3 consecutive flips?

(A) 0.125
(B) 0.25
(C) 0.375
(D) 0.50
(E) 0.666
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Don't be afraid to take a flying leap of faith.. If you risk nothing, than you gain nothing...

Last edited by TeHCM on 27 Dec 2005, 00:45, edited 2 times in total.
Director
Joined: 14 Sep 2005
Posts: 994
Location: South Korea
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Re: Probability: Coins [#permalink]  26 Dec 2005, 18:18
TeHCM wrote:
If a coin has a probability of landing heads up or tails each time it is flipped, what is the probability that the coin will land heads up exactly twice in 3 consecutive flips?

(A) 0.125
(B) 0.25
(C) 0.375
(D) 0.50
(E) 0.666

3C2/3! = 3/8 = 0.375

However, there has to be one condition that the probability of landing heads up is 1/2.
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VP
Joined: 06 Jun 2004
Posts: 1059
Location: CA
Followers: 2

Kudos [?]: 46 [0], given: 0

Or we could utilize binomial distribution here....

C(3,2)*(1/2)^2*(1-1/2)^1 = 3*1/4*1/2 = 3/8 = 0.375

OA is C.

Thanks
_________________

Don't be afraid to take a flying leap of faith.. If you risk nothing, than you gain nothing...

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If a coin has a probability of landing heads up or tails

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