Xiaoping reads a story book, and has read 40% of the whole book, leaving 90 pages unread. What percentage of the number of pages that have not been read is the number of pages that have not been read?
小平看一本故事书，已经看了全书的40%，还剩90页没有看．没看的页数是看完的页数的百分之几？
<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (2/5)</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">(3/5) / (2/5)</gadget>
<output>3/2 = around 1.5</output>

<result>3/2 = around 1.5</result>