A used-book dealer sells paperback books at 3 times dealer's cost and hardback books at 4 times the dealer's cost. Last week, the dealer sold a total of 140 books, each of which had cost the dealer $1. If the gross profit (sales revenue minus the dealer's cost) on the sale of all of these books was $300, how many of the books sold were paperbacks?  Answers.
A) 100	B) 110	C) 120	D) 130	E) 140
The dealer earns a profit of $2 per paperback and $3 per hardback.   If all 140 books were paperbacks, the dealer would earn a profit of $280.   Since the actual profit was $300, the dealer must have sold 20 hardbacks.   Then the number of paperbacks sold was 140-20= 
<gadget id="calculator">140-20</gadget>
<output>120</output>
120.   The answer is 120.
<result>C</result>
A used-book dealer sells paperback books at 3 times dealer's cost and hardback books at 4 times the dealer's cost. Last week, the dealer sold a total of 140 books, each of which had cost the dealer $1. If the gross profit (sales revenue minus the dealer's cost) on the sale of all of these books was $300, how many of the books sold were paperbacks?