document.write( "Question 1206099: A textbook store sold a combined total of 215 psychology and history textbooks in a week. The number of psychology textbooks sold was 57 more than the number of history textbooks sold. How many textbooks of each type were sold? \n" ); document.write( "

Algebra.Com's Answer #843321 by ikleyn(52784) $\"\"$ $\"About$

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\n" ); document.write( "A textbook store sold a combined total of 215 psychology and history textbooks in a week.
\n" ); document.write( "The number of psychology textbooks sold was 57 more than the number of history textbooks sold.
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\n" ); document.write( "\n" ); document.write( " This problem can be solved MENTALLY.
\n" ); document.write( " Below I show you how to do it.\r
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document.write( "For a minute, from the total of 215 textbooks, take off mentally 57 psychology textbooks.\r\n" );
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document.write( "Then you will have new collection of 215-57 = 158 textbooks,\r\n" );
document.write( "and in this updated collection, the number of psychology textbook will be the same \r\n" );
document.write( "as the number of history textbooks.\r\n" );
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document.write( "Hence, the number of history textbook is half of 158, i.e. 158/2 = 79 textbooks.\r\n" );
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document.write( "Then the number of psychology textbook in the original collection is 79 + 57 = 136.\r\n" );
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document.write( "ANSWER.  136 psychology textbooks and 79 history textbooks.\r\n" );
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\n" ); document.write( "\n" ); document.write( "Solved mentally, without using equations.\r
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