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You flip three coins. What is the probability that you get at least two tails, given that you get at least one tail?
 one year ago
 one year ago
You flip three coins. What is the probability that you get at least two tails, given that you get at least one tail?
 one year ago
 one year ago

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PhoenixFireBest ResponseYou've already chosen the best response.1
It's heads or tails, so it's a binomial distribution. So we use the formula: \[{n \choose r}{p^r}{(1p)^{nr}}\] where n is the number of trials (3) and r is the number of successes (tails). \[{3 \choose 2}{0.5^2}{(10.5)^{32}}={3 \choose 2}{(0.25)}{(0.5)}={3 \choose 2}(0.125)\] \[{n \choose r}={n! \over {r!(nr)!}}={3! \over 2!1!}={{1*2*3} \over 1*2*1}=3\] So, \[3*0.125=0.375=P(X=2)\]
 one year ago
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