The third-grade students have a mathematics competition. It is stipulated that 5 points will be awarded for each correct answer, and 5 points will be deducted for each incorrect answer. No points will be awarded for no answers. There were 20 questions in the test paper. Li Ming answered every question and got 80 points. How many questions did he get wrong?
三年级学生进行数学竞赛，规定答对一题得5分，答错一题倒扣5分，不答不得分．试卷上共有20道题，李明每道题都解答了，得了80分．他算错了几道题？
<gadget id="calculator">20 * 5</gadget>
<output>100</output>

<gadget id="calculator">100 - 80</gadget>
<output>20</output>

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

<gadget id="calculator">20 / 10</gadget>
<output>2</output>

<result>2</result>