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# John throws a coin until a series of three consecutive heads

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Director
Joined: 14 Jan 2007
Posts: 775

Kudos [?]: 172 [0], given: 0

John throws a coin until a series of three consecutive heads [#permalink]

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30 Jun 2007, 09:06
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Question Stats:

100% (00:00) correct 0% (00:00) wrong based on 1 sessions

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John throws a coin until a series of three consecutive heads or three consecutive tails appears. What is the probability that the game will end after the fourth throw?

1. 1/16
2. 2/16
3. 3/16
4. 4/16
5. 6/16

Kudos [?]: 172 [0], given: 0

Senior Manager
Joined: 04 Jun 2007
Posts: 345

Kudos [?]: 33 [0], given: 0

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30 Jun 2007, 09:16
vshaunak@gmail.com wrote:
John throws a coin until a series of three consecutive heads or three consecutive tails appears. What is the probability that the game will end after the fourth throw?

1. 1/16
2. 2/16
3. 3/16
4. 4/16
5. 6/16

B for me.

The probability of getting heads=probability of getting tails=1/2

If the game ends after the fourth throw, there are two possibilities.
T,H,H,H or H,T,T,T.

Therefore, required probability= 2 * [(1/2)^4] = 2/16 (or 1/8 )

Kudos [?]: 33 [0], given: 0

Re: PS Probability   [#permalink] 30 Jun 2007, 09:16
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