A book has a total of 100 pages. I read (1/4) of it for the first time, and 20 pages for the second time. How many pages are left?
一本书共100页，第一次看了它的(1/4)，第二次看了20页，还剩多少没有看．
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">100 * (1/4)</gadget>
<output>25</output>

<gadget id="calculator">100 - 25 - 20</gadget>
<output>55</output>

<gadget id="calculator">55 / 100</gadget>
<output>11/20 = around 0.55</output>

<result>11/20 = around 0.55</result>