Question 971283
Let {{{ c }}} = the cost of the 200 books
{{{ c/200 }}} = the cost of each book
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{{{ 80*( c/200 ) }}} = the cost of the 80 
books that he sold
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{{{ 1.15*( 80*( c/200 )) }}} = his selling
price of the 80 books
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{{{ 1.5*( 120*( c/200 )) }}} = his selling
price of the remaining books
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I can say:
{{{ 1.15*( 80*( c/200 )) + 1.5*( 120*( c/200 )) = 27200 }}}
{{{ 1.15*.4c + 1.5*.6c = 27200 }}}
{{{ .46c + .9c = 27200 }}}
{{{ 1.36c = 27200 }}}
{{{ c = 20000 }}} 
answer is (3)