Xiao Zhang reads a story book, and has read 40% of the whole book, leaving 90 pages unread. By what percentage is the number of unread pages greater than the number of finished pages?
小张看一本故事书，已经看了全书的40%，还剩90页没看．没看的页数比看完的页数多百分之几？
<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (2/5) - (2/5)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/5) / (2/5)</gadget>
<output>1/2 = around 0.5</output>

<result>1/2 = around 0.5</result>