Xiao Ming reads a book, reads 25% of the whole book on the first day, reads 20 more pages on the second day than the first day, and finishes the remaining 50 pages on the third day. How many pages does this book have?
小明看一本书，第一天看了全书的25%，第二天比第一天多看了20页，剩下50页第三天看完，这本书共有多少页？
<gadget id="calculator">20 + 50</gadget>
<output>70</output>

<gadget id="calculator">25 / 100</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 - (1/4) - (1/4)</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">70 / (1/2)</gadget>
<output>140</output>

<result>140</result>