Xiaohong reads a book. She reads 40% of the total pages of the book on the first day, 12 pages on the second day, and half of the total pages of the book on the third day. How many pages does this book have?
小红看一本书，第一天看了这本书总页数的40%，第二天看了12页，第三天又看了这本书总页数的一半，正好看完．这本书共有多少页？
<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

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

<gadget id="calculator">1 - (2/5) - (1/2)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">12 / (1/10)</gadget>
<output>120</output>

<result>120</result>