There are 50 students in a class. In a test, 25 students answered the first question correctly, 20 students answered the second question correctly, and 10 students answered both questions correctly. How many students got neither question right?
某班有50名同学，在一次测验中答对第一题的有25人，答对第二题的有20人，两题都答对的有10人，则有几名同学两题都不对？
<gadget id="calculator">50 - 25 - 20</gadget>
<output>5</output>

<gadget id="calculator">5 + 10</gadget>
<output>15</output>

<result>15</result>