Xiao Ming reads a story book, reads 20 pages on the first day, and reads the rest (1/3) on the second day. At this time, the number of pages that have not been read is equal to the number of pages that have been read. How many pages does this book have? (use at least 3 methods)
小明看一本故事书，第一天看了20页，第二天看了余下的(1/3)，这时未看的与已看的页数相等，这本书共有多少页？(至少用3种方法)
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">20 * (1/3)</gadget>
<output>20/3 = around 6.666667</output>

<gadget id="calculator">20 - (20/3)</gadget>
<output>40/3 = around 13.333333</output>

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

<gadget id="calculator">1 - (1/3) - (1/2)</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">(40/3) / (1/6)</gadget>
<output>80</output>

<result>80</result>