There are 37 people in a class going on a trip, 20 wear hats and 28 wear shorts. How many of them wear hats and shorts at most?
某班有37人去旅行，戴帽子的有20人，穿短裤的有28人，问其中最多有几人同时戴帽子及穿短裤的呢？
<gadget id="calculator">28 - 37</gadget>
<output>-9</output>

<gadget id="calculator">20 + (-9)</gadget>
<output>11</output>

<result>11</result>