document.write( "Question 1132005: Two fair coins were tossed and it is known that at least one was a head. Find the probability that they were both heads.
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Algebra.Com's Answer #748797 by ikleyn(52777) $\"\"$ $\"About$

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document.write( "When two fair coins are tossed, the space of events consists of four elements\r\n" );
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document.write( "HH   (*)\r\n" );
document.write( "HT   (*)\r\n" );
document.write( "TH   (*)\r\n" );
document.write( "TT\r\n" );
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document.write( "Of them, the sub-space consisting of three elements, marked (*) in the list, is the sub-space  \"at least one is head\".\r\n" );
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document.write( "In this sub-space of three elements, only one HH is \"two heads\", or, equivalently, \"both heads\".\r\n" );
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document.write( "Therefore, the conditional probability under the question is  .\r\n" );
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