A book Xiaoming has read (1/4) of the whole book, if he reads 20 more pages, he can read half of the book. How many pages does this book have?
一本书小明已经看了全书的(1/4)，如果再看20页，就可以看完全书的一半，这本书共有多少页？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

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

<gadget id="calculator">(1/2) - (1/4)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">20 / (1/4)</gadget>
<output>80</output>

<result>80</result>