There are 50 students in a certain class, 27 can swim, 18 can gymnastics, and 15 can neither. So how many people can both swim and gymnastics?
某班有50人，会游泳的有27人，会体操的有18人，都不会的有15人．那么既会游泳又会体操的有几人．
<gadget id="calculator">15 - 50</gadget>
<output>-35</output>

<gadget id="calculator">27 + 18 + (-35)</gadget>
<output>10</output>

<result>10</result>