50 students answered questions A and B, 12 of them did not answer question A correctly, and 30 students answered both question A and question B correctly. How many people can answer both questions A and B correctly?
50个学生解答A、B两题，其中没答对A题的有12人，答对A题的且没答对B题的有30人．那么A、B两题都答对的有多少人．
<gadget id="calculator">50 - 12 - 30</gadget>
<output>8</output>

<result>8</result>