There are 3 classes in the third grade with an average of 40 students in each class. There are 38 people in class one, 40 people in class two, how many people are in class three?
三年级3个班平均每班有学生40人．其中一班有38人，二班有40人，三班有多少人？
<gadget id="calculator">40 * 3</gadget>
<output>120</output>

<gadget id="calculator">38 + 40</gadget>
<output>78</output>

<gadget id="calculator">120 - 78</gadget>
<output>42</output>

<result>42</result>