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# If John flips a coin three times, what is the probability that he will

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Retired Moderator
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Joined: 18 Jun 2009
Posts: 1296
Concentration: Strategy, General Management
GMAT 1: 680 Q48 V34
If John flips a coin three times, what is the probability that he will [#permalink]

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24 Apr 2010, 00:28
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1. If John flips a coin three times, what is the probability that he will get a heads at least once?

2. If John flips a coin three times, what is the probability that it will turn up heads at least twice?
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Retired Moderator
Status: The last round
Joined: 18 Jun 2009
Posts: 1296
Concentration: Strategy, General Management
GMAT 1: 680 Q48 V34
Re: If John flips a coin three times, what is the probability that he will [#permalink]

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24 Apr 2010, 05:03
Actually, I want to know the concept, so can you kindly explain your answers in detail. There is no official answer as I just made these questions.
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Re: If John flips a coin three times, what is the probability that he will [#permalink]

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24 Apr 2010, 05:31
Hussain15 wrote:
1. If John flips a coin three times, what is the probability that he will get a heads at least once?

2. If John flips a coin three times, what is the probability that it will turn up heads at least twice?

1. If John flips a coin three times, what is the probability that he will get a heads at least once?

$$P(H\geq{1})=1-P(H=0)=1-(\frac{1}{2})^3=\frac{7}{8}$$

2. If John flips a coin three times, what is the probability that it will turn up heads at least twice?

$$P(H\geq{2})=P(H=2)+P(H=3)=\frac{3!}{2!}*(\frac{1}{2})^2*\frac{1}{2}+(\frac{1}{2})^3=\frac{1}{2}$$
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Re: If John flips a coin three times, what is the probability that he will   [#permalink] 24 Apr 2010, 05:31
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