Ding Ding has 15 empty ping-pong boxes, put 40 ping-pong balls in every 5 boxes, how many empty ping-pong boxes does Ding Ding have left?
小丁丁有15个空的乒乓球盒，将40个乒乓球按每5个放一盒，小丁丁还剩下几个空的乒乓球盒？
<gadget id="calculator">40 / 5</gadget>
<output>8</output>

<gadget id="calculator">15 - 8</gadget>
<output>7</output>

<result>7</result>