The teacher gave two thinking questions to the students in the class. After correcting, he found that: everyone in the class got at least one question right, 30 people got the first question right, 25 people got the second question right, and they got both questions right There are 13 people. Please do the math, how many students are there in the class?
老师给班上同学出了两道思考题，批改后发现：全班每人至少做对一道，第1道做对的有30人，第2道做对的有25人，两道都做对的有13人．请你算一算，班上一共有学生多少人？
<gadget id="calculator">25 - 13</gadget>
<output>12</output>

<gadget id="calculator">30 + 12</gadget>
<output>42</output>

<result>42</result>