A book has 80 pages. I read the whole book (1/4) first, and then read 15 pages. How much of the whole book is left.
一本书80页，先看了全书的(1/4)，又看了15页，还剩下全书的多少．
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">15 / 80</gadget>
<output>3/16 = around 0.1875</output>

<gadget id="calculator">1 - (1/4) - (3/16)</gadget>
<output>9/16 = around 0.5625</output>

<result>9/16 = around 0.5625</result>