document.write( "Question 945594: A bookcase contains 6 different math books and 12 different physics books. If a student randomly selects two of these books, then what is the probability he or she selects two books from the same subject?
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Algebra.Com's Answer #577035 by Edwin McCravy(20054)\"\" \"About 
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A bookcase contains 6 different math books and 12 different physics books. If a
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document.write( "There are 2 ways to do this problem.  Take your pick:\r\n" );
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document.write( "First way:\r\n" );
document.write( "1. Calculate the number of ways to select ANY two books. \r\n" );
document.write( "   18 choose 2 = 18C2 = 153.\r\n" );
document.write( "2. Subtract the number of ways to select a math book and a physics book.\r\n" );
document.write( "   Choose the math book 6 ways and the physics book 12 ways, that's 6*12=72\r\n" );
document.write( "3. No. of ways: 153-72 = 81 ways.\r\n" );
document.write( "Probability 81/153 = 9/17\r\n" );
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document.write( "Second way:\r\n" );
document.write( "Case 1: Select two math books \"6 choose 2\" = 6C2 = 15 ways.\r\n" );
document.write( "Case 2: Select two physics books \"12 choose 2\" = 12C2 = 66 ways.\r\n" );
document.write( "Total: 15+66 = 81 ways. \r\n" );
document.write( "Calculate the number of ways to select ANY two books. 18C2 = 153\r\n" );
document.write( "Probability: 81/153 = 9/17\r\n" );
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document.write( "Edwin
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