fifth grade elementary school held a quick-calculation competition. A total of 100 questions were given. A did 4 questions per minute, and B used 1.5 points less for every 20 questions than A calculated the same number of questions. When B finished 100 questions, How many questions does A still have to do?
某小学五年级进行速算比赛，共出了100道题，甲每分做4道题，乙每算出20道题比甲算出同样多的题少用1.5分，则乙做完100道题时，甲还有多少道题没做．
<gadget id="calculator">100 / 20</gadget>
<output>5</output>

<gadget id="calculator">20 / 4</gadget>
<output>5</output>

<gadget id="calculator">5 - 1.5</gadget>
<output>3.5</output>

<gadget id="calculator">5 * 3.5</gadget>
<output>17.5</output>

<gadget id="calculator">4 * 17.5</gadget>
<output>70</output>

<gadget id="calculator">100 - 70</gadget>
<output>30</output>

<result>30</result>