There are 20 multiple-choice questions in a math test paper. For each correct answer, 5 points will be awarded, and one point will be deducted for each question that is not answered or answered incorrectly. A student gets 82 points. How many questions did he answer correctly?
一份数学试卷共20道选择题，每答对一题得5分，不答或答错一题扣一分，一位同学得了82分，他答对了多少道题．
<gadget id="calculator">20 * 5</gadget>
<output>100</output>

<gadget id="calculator">100 - 82</gadget>
<output>18</output>

<gadget id="calculator">5 + 1</gadget>
<output>6</output>

<gadget id="calculator">18 / 6</gadget>
<output>3</output>

<gadget id="calculator">20 - 3</gadget>
<output>17</output>

<result>17</result>