A story book, 15 pages have been read, which accounts for exactly 30% of the whole book, how many pages are left?
一本故事书，已经看15页，正好占全书的30%，还剩下多少页？
<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">15 / (3/10)</gadget>
<output>50</output>

<gadget id="calculator">1 - (3/10)</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">50 * (7/10)</gadget>
<output>35</output>

<result>35</result>