Ning Ning reads a story book. She read the whole book on the first day (5/18), and the whole book on the second day (4/15). How much of the book is left unread?
宁宁看一本故事书，第一天看了全书的(5/18)，第二天看了全书的(4/15)，还剩这本书的几分之几没看？
<gadget id="calculator">5 / 18</gadget>
<output>5/18 = around 0.277778</output>

<gadget id="calculator">4 / 15</gadget>
<output>4/15 = around 0.266667</output>

<gadget id="calculator">1 - (5/18) - (4/15)</gadget>
<output>41/90 = around 0.455556</output>

<result>41/90 = around 0.455556</result>