The bookstore wants to send 980 textbooks to the school, each box contains 50 books, 18 boxes have been packed, how many books are not packed?
书店要把980本教科书送到学校去，每箱装50本，已装了18箱，没有装箱的是多少本？
<gadget id="calculator">50 * 18</gadget>
<output>900</output>

<gadget id="calculator">980 - 900</gadget>
<output>80</output>

<result>80</result>