document.write( "Question 76116: A coin is tossed 9 times. What is the probability that the coin will land heads at least 7 times? \n" ); document.write( "
Algebra.Com's Answer #54646 by Edwin McCravy(20055)\"\" \"About 
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document.write( "A coin is tossed 9 times. What is the \r\n" );
document.write( "probability that the coin will land heads \r\n" );
document.write( "at least 7 times?\r\n" );
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document.write( "This is a binomial probability. You can \r\n" );
document.write( "find it directly from a binomial\r\n" );
document.write( "table, a TI-83 calculator, or entirely \r\n" );
document.write( "from the formula.\r\n" );
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document.write( "Using the formula: \r\n" );
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document.write( "\"C%28n%2Cx%29p%5En%2Aq%5E%28n-x%29\"\r\n" );
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document.write( "gives the probability that in n trials \r\n" );
document.write( "there will be exactly x successes\r\n" );
document.write( "where\r\n" );
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document.write( "p = the probability of one success in \r\n" );
document.write( "one trial and q = 1-p = the probability \r\n" );
document.write( "of one failure in one trial.\r\n" );
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document.write( "\"C%28n%2Cx%29+=+n%21%2F%28x%21%28n-x%29%21%29\"\r\n" );
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document.write( "In the case of a coin, p = 1/2 and q = 1 - 1/2 = 1/2\r\n" );
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document.write( "P(coin landing heads at least 7 times out of 9 tosses) =\r\n" );
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document.write( "P(coin landing exactly 7 times out of 9) +   \r\n" );
document.write( "       P(coin landing exactly 8 times out of 9) +\r\n" );
document.write( "              P(coin landing exactly 9 times out of 9) =\r\n" );
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document.write( " =\r\n" );
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document.write( "\"C%289%2C7%29%281%2F2%29%5E9+%2B+C%289%2C8%29%281%2F2%29%5E9+%2B+C%289%2C9%29%281%2F2%29%5E9\" =\r\n" );
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document.write( "Factor out \"%281%2F2%29%5E9\"\r\n" );
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document.write( "\"%281%2F2%29%5E9%2A%28C%289%2C7%29+%2B+C%289%2C8%29+%2B+C%289%2C9%29%29\" =\r\n" );
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document.write( "\"%281%2F512%29%2A%28C%289%2C7%29+%2B+C%289%2C8%29+%2B+C%289%2C9%29%29\"\r\n" );
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document.write( "which gives the desired probability.\r\n" );
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document.write( "To calculate this we need:\r\n" );
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document.write( "Therefore the desired probability =\r\n" );
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document.write( "----------------------------------------------\r\n" );
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document.write( "If you use a TI-83 or TI-84 calculator, type in\r\n" );
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document.write( "1 - binomcdf(9,1/2,6)\r\n" );
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document.write( "then press ENTER and you get .08984375\r\n" );
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document.write( "To get binomcdf( , press 2nd, then VARS, then \r\n" );
document.write( "scroll down to binomcdf( , then press ENTER.\r\n" );
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document.write( "Edwin

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