Question 1172386
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Let x be the number of dozens of exercise books bought.


Then the number of books bought was  12x.


The number of books sold is  (12x - 13). 


The money equation for the profit is easy to write.  It is


    (12x-13)*32 = 12x*20 + 88.



From this equation


    12x*32 - 12x*20  = 88 + 13*32,   or

    (12*32 - 12*20)x = 504

         144x        = 504

            x        = {{{504/144}}} = 3.5.


<U>ANSWER</U>.  3.5  dozens of books were bought.

         //  3.5 dozens is 12*3.5 = 42 books, so there is no reason to worry about the integer number of books.
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Solved.