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If a certain coin is flipped, the probability that the coin

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Joined: 06 Nov 2008
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If a certain coin is flipped, the probability that the coin [#permalink]

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09 Nov 2008, 19:19
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If a certain coin is flipped, the probability that the coin will land heads is 1/2. If the coin is flipped 5 times, what is the probability that it will land heads up on the first 3 flips and not on the last 2 flips?

A. 3/5
B. 1/2
C. 1/5
D. 1/8
E. 1/32
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Joined: 07 Nov 2008
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09 Nov 2008, 22:26
haichao wrote:
If a certain coin is flipped, the probability that the coin will land heads is 1/2. If the coin is flipped 5 times, what is the probability that it will land heads up on the first 3 flips and not on the last 2 flips?

A. 3/5
B. 1/2
C. 1/5
D. 1/8
E. 1/32

the probability of the first 3 flips which is heads up is (1/2)^3
and the probability of the first 3 flips which is not heads up is (1/2)^2

multiple them together,
(1/2)^5

E

btw, if we want the side of n times of coin flipp to be what we wanted to be, then the probability is (1/2)^n
Re: coins---28   [#permalink] 09 Nov 2008, 22:26
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