In the third grade, 92 children participated in the cultural performance, among which 68 participated in the chorus and 64 participated in the dance performance. Each of them participated in at least one performance. How many children in the third grade participated in both the chorus and the dance performance?
三年级有92个小朋友参加文艺会演，其中参加大合唱的有68人，参加舞蹈演出的有64人，每人至少参加一项表演，三年级既参加大合唱又参加舞蹈演出的有几人？
<gadget id="calculator">64 - 92</gadget>
<output>-28</output>

<gadget id="calculator">68 + (-28)</gadget>
<output>40</output>

<result>40</result>