document.write( "Question 493384: What is the probability of obtaining exactly eight heads in nine flips of a coin, given that at least one is a head?\r
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\n" ); document.write( "\n" ); document.write( "Can I get a little bit of help this evening? This one is too hard to try and solve on my own.Thanks very much! \n" ); document.write( "
Algebra.Com's Answer #335338 by stanbon(75887)\"\" \"About 
You can put this solution on YOUR website!
What is the probability of obtaining exactly eight heads in nine flips of a coin, given that at least one is a head?
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\n" ); document.write( "P(8 H in 9 flips | >= 1 H)
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\n" ); document.write( "= P(8 H in 9 flips AND >= 1 H)/P(at least one H)
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\n" ); document.write( "Ans = P(8 H in 9 flips) / P(at least one H)
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\n" ); document.write( "P(8 H in 9 flips) = 9C8(1/2)^9 = 9/2^9
\n" ); document.write( "P(at least one H) = 1 - P(no H) = 1 - (1/2)^9
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\n" ); document.write( "Therefore: Ans = [9/2^9]/(1 - (1/2)^9)
\n" ); document.write( "= [9/2^9]/[(2^9-1)/2^9]
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\n" ); document.write( "= 9/[2^9-1]
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\n" ); document.write( "Cheers,
\n" ); document.write( "Stan H.
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