There are 20 true or false questions in a math contest, each correct answer is worth 5 points, and each wrong answer is deducted 1.5 points. Miao Xiang scored 87 points, how many questions did he get wrong?
一次数学竞赛共有20道判断题，每答对一道题得5分，每答错一题倒扣1.5分．妙想得了87分，他答错了几道题？
<gadget id="calculator">5 * 20</gadget>
<output>100</output>

<gadget id="calculator">100 - 87</gadget>
<output>13</output>

<gadget id="calculator">5 + 1.5</gadget>
<output>6.5</output>

<gadget id="calculator">13 / 6.5</gadget>
<output>2</output>

<result>2</result>