There are 29 students in the third grade, 18 students participated in the singing group, 16 students participated in the dance group, and how many students participated in both.
三年级有学生29人，参加歌唱组的有18人，参加舞蹈组的有16人，两项都参加的有多少人．
<gadget id="calculator">16 - 29</gadget>
<output>-13</output>

<gadget id="calculator">18 + (-13)</gadget>
<output>5</output>

<result>5</result>