When Xiao Ming reads a book, when he finishes reading 70% of the book, it happens to be 40 pages more than half of the book. How many pages does this book have?
小明读一本书，当读完这本书的70%时，恰好比这本书的一半多40页，这本书共多少页？
<gadget id="calculator">70 / 100</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(7/10) - (1/2)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">40 / (1/5)</gadget>
<output>200</output>

<result>200</result>