If you read 40% of a book on the first day and 35% on the second day, and read 5 pages less on the second day than on the first day, how many pages are there in this book?
一本书，第一天看了40%，第二天看了35%，第二天比第一天少看了5页，这本书共有多少
<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">35 / 100</gadget>
<output>7/20 = around 0.35</output>

<gadget id="calculator">(2/5) - (7/20)</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">5 / (1/20)</gadget>
<output>100</output>

<result>100</result>