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document.write( "If the 13 pupils are A,B,C,D,E,F,G,H,I,J,K,L,M\r\n" );
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document.write( "First consider the three groups to be Group A of 4, Group B of 5, and\r\n" );
document.write( "Group C of 4.\r\n" );
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document.write( "Choose the pupils for Group A:\r\n" );
document.write( "That's 13 pupils choose 4, or 13C4\r\n" );
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document.write( "Choose the pupils for Group B:\r\n" );
document.write( "That's 9 remaining pupils choose 5, or 9C5\r\n" );
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document.write( "Choose the pupils for Group C:\r\n" );
document.write( "That's 4 remaining pupils choose 4, or 4C4\r\n" );
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document.write( "That would be (13C4)(9C4)(4C4) = (715)(126)(1) = 90090\r\n" );
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document.write( "if such groupings as these 2:\r\n" );
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document.write( "Group A = {C,G,I,M}, Group B = {B,D,E,J,L}, Group C ={A,F,H,K} \r\n" );
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document.write( "and \r\n" );
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document.write( "Group A = {A,F,H,K}, Group B = {B,D,E,J,L}, Group C ={C,G,I,M}\r\n" );
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document.write( "were distinguishable (with Groups A and C swapped).\r\n" );
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document.write( "But they probably aren't, so we will divide 90090 by 2 and get\r\n" );
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document.write( "Answer = 45045.\r\n" );
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document.write( "Edwin \n" );
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