There are 50 students in a class, 27 of them can swim, 18 can do gymnastics, and 15 can neither swim nor gymnastics. How many people can both gymnastics and swim?
某班学生共50人，其中27人会游泳，会体操的有18人，游泳、体操都不会的有15人．既会体操又会游泳的有多少人．
<gadget id="calculator">15 - 50</gadget>
<output>-35</output>

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

<result>10</result>