For a book, Li Na read (1/5) of the whole book on the first day, (1/4) of the whole book on the second day, read the sum of the previous two days on the third day, and read the whole book on the third day What percentage? How much of the book is left unread?
一本书，李娜第一天看了全书的(1/5)，第二天看了全书的(1/4)，第三天看的是前两天之和，第三天看了全书的几分之几？还剩全书的几分之几没有看？
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">9 / 20</gadget>
<output>9/20 = around 0.45</output>

<gadget id="calculator">1 - (1/5) - (1/4) - (9/20)</gadget>
<output>1/10 = around 0.1</output>

<result>1/10 = around 0.1</result>