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October 6th, 2013, 12:14 PM   #1
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simple probability Q

Two coins are tossed. What is the conditional probability that two heads result given that there is a t least one head?

let S be the sample space

S = {{HH},{HT},{TH,{TT}}

P(HH|HT,TH,HH) = P(HH n HT,TH,HH)/P(HT,TH,HH) = (1/4 * 3/4) / (3/4) = 1/4

is this correct? I'm finding it hard to determine what the question is actually asking
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October 6th, 2013, 05:21 PM   #2
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Re: simple probability Q

Quote:
Originally Posted by lun123
Two coins are tossed. What is the conditional probability that two heads result given that there is a t least one head?

let S be the sample space

S = {{HH},{HT},{TH,{TT}}

P(HH|HT,TH,HH) = P(HH n HT,TH,HH)/P(HT,TH,HH) = (1/4 * 3/4) / (3/4) = 1/4

is this correct? I'm finding it hard to determine what the question is actually asking
It is incorrect. HH is not independent of (HT,TH,HH).
The numerator should be P(HH) = 1/4, so the net result = 1/3.
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