In a class of 40 students in a math test, 23 people answered the first question correctly, 27 people answered the second question correctly, and 17 people answered both questions correctly. Ask how many students can answer both questions incorrectly.
某班40位同学在一次数学考试测验中，答对第一题的有23人，答对第二题的有27人，两题都答对的有17人，问有多少个同学两题都答不对．
<gadget id="calculator">27 - 17</gadget>
<output>10</output>

<gadget id="calculator">23 + 10</gadget>
<output>33</output>

<gadget id="calculator">40 - 33</gadget>
<output>7</output>

<result>7</result>