Xiao Ming reads a story book. He read 20 pages on the first day and 30 pages on the second day, leaving 75% of the book unread. How many pages does this book have?
小明读一本故事书，第一天读了20页，第二天读了30页，还剩75%没有读．这本书一共有多少页？
<gadget id="calculator">20 + 30</gadget>
<output>50</output>

<gadget id="calculator">75 / 100</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">1 - (3/4)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">50 / (1/4)</gadget>
<output>200</output>

<result>200</result>