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

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Senior Manager
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If a certain coin is flipped, the probability that the coin [#permalink]  05 May 2006, 22:04
If a certain coin is flipped, the probability that the coin will land heads is 1/2. If the coin is flipped 2 times, what is the probability that it will land heads up at least one time?
Senior Manager
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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 2 times, what is the probability that it will land heads up at least one time?

Hi,
Total outcomes: HH, HD, DD, DH
3 of them satisfies us, thus the answer is needed outcomes/total outcomes = 3/4

P.S.:
When prob.question invloves words such as "at least", sometimes it is easier to find probabitlity by substracting negative outcomes from total outcomes: 1 - NO/TO
Intern
Joined: 02 May 2006
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I have tough time with prob. qstns...learning as i go..I think it is 1/4? anyone?
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Let P(H) and P(T) denote the probabilities of a head and a tail respectively. The reqd. prob
= P(H)P(T) + P(T)P(H) + P(H)P(H)
= (1/4) x 3
= 3/4
VP
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1 - (2C2*(1/2)^2) = 3/4
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P(tails) = 1/2

P(tails) AND P(tails) = 1/4

P(at least one head) = 3/4
VP
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Agreed its 3/4

HH, HT and TH
VP
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Re: flip of a coin [#permalink]  08 May 2006, 20:30
getzgetzu wrote:
If a certain coin is flipped, the probability that the coin will land heads is 1/2. If the coin is flipped 2 times, what is the probability that it will land heads up at least one time?

total = 4
both tails = 1

= 1- p(t) = 1-1/4 = 3/4
Re: flip of a coin   [#permalink] 08 May 2006, 20:30
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