20 students line up to do exercises, there are 11 people in front of Xiaohong, how many people are behind Xiaohong.
20个同学排成队做操，小红前面有11人，小红的后面还有多少人．
<gadget id="calculator">20 - 11 - 1</gadget>
<output>8</output>

<result>8</result>