Xiao Ming reads a 100-page extra-curricular book. He reads (1/4) of the whole book on the first day and (1/5) of the whole book on the second day. How much of this book is left unread?
小明读一本100页的课外书，第一天读了全书的(1/4)，第二天读了全书的(1/5)．这本书还剩下几分之几没有读？
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (1/4) - (1/5)</gadget>
<output>11/20 = around 0.55</output>

<result>11/20 = around 0.55</result>