Read a book by force, read 20% of the whole book in the morning, read 20 pages more in the afternoon than in the morning, and still have half of it unread, how many pages does this book have?
强强读一本书，上午读了全书的20%，下午比上午多读了20页，这时还有一半没有读，这本书有多少页？
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/5) * 2</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">50 / 100</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">20 / (1/10)</gadget>
<output>200</output>

<result>200</result>