A used-book dealer sells paperback books at 3 times the dealer's cost and hardback books at 4 times the dealer's cost. Last week, the dealer sold a total of 130 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?
Choose one
A) 40 B) 60 C) 75 D) 90 E) 100
The dealer earns a profit of $2 per paperback and $3 per hardback.   If all 130 books were paperbacks, the dealer would earn a profit of $260.   Since the actual profit was $300, the dealer must have sold 40 hardbacks.   Then the number of paperbacks sold was 130-40= 
<gadget id="calculator">130-40</gadget>
<output>90</output>
90.   The answer is 90.
<result>D</result>
A used-book dealer sells paperback books at 3 times the dealer's cost and hardback books at 4 times the dealer's cost. Last week, the dealer sold a total of 130 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?