There are 36 students in a class in a test, 25 of them answered the first question correctly, 23 of them answered the second question correctly, and 15 of them answered both questions correctly. How many students can answer both questions incorrectly?
某班有36个同学在一项测试中，答对第一题的有25人，答对第二题的人有23人，两题都答对的有15人．两题都答不对的同学有多少人．
<gadget id="calculator">23 - 15</gadget>
<output>8</output>

<gadget id="calculator">25 + 8</gadget>
<output>33</output>

<gadget id="calculator">36 - 33</gadget>
<output>3</output>

<result>3</result>