document.write( "Question 1114136: In how many ways 7 different books can be arranged on a shelf? In how man many ways will a specified book be (I) at the centre? (II)
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Algebra.Com's Answer #729137 by ikleyn(52778)\"\" \"About 
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document.write( "(I)  It is VERY STANDARD introductory problem on PERMUTATIONS for beginners.\r\n" );
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document.write( "     The answer is  7! = 1*2*3*4*5*6*7.\r\n" );
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document.write( "     The standard solution (=mantra) is this:\r\n" );
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document.write( "         You can put any of the 7 books in the 1-st position in 7 ways.\r\n" );
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document.write( "         You can put any of the remaining 6 books in the 2-nd position in 6 ways.\r\n" );
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document.write( "         You can put any of the remaining 5 books in the 3-rd position in 5 ways.\r\n" );
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document.write( "         . . . and so on . . . \r\n" );
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document.write( "         You can put any of the remaining 2 books in the 6-th position in 2 ways.\r\n" );
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document.write( "         Finally, you can put the last remaining 1 book in the 7-th position in 1 way only (there is nothing to select from at this step . . . ).\r\n" );
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document.write( "         Since these selections/options are independent, you have  7! = 7*6*5*4*3*2*1  ways, in all.\r\n" );
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\n" ); document.write( "On Permutations,  see the lessons\r
\n" ); document.write( "\n" ); document.write( "    - Introduction to Permutations\r
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\n" ); document.write( "\n" ); document.write( "    - OVERVIEW of lessons on Permutations and Combinations\r
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\n" ); document.write( "\n" ); document.write( "Also,  you have this free of charge online textbook in ALGEBRA-II in this site\r
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\n" ); document.write( "\n" ); document.write( "The referred lessons are the part of this online textbook under the topic  \"Combinatorics: Combinations and permutations\". \r
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\n" ); document.write( "\n" ); document.write( "Save the link to this textbook together with its description\r
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\n" ); document.write( "\n" ); document.write( "Free of charge online textbook in ALGEBRA-II
\n" ); document.write( "https://www.algebra.com/algebra/homework/complex/ALGEBRA-II-YOUR-ONLINE-TEXTBOOK.lesson\r
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