When Xiao Ming reads a storybook, he has already read 40% of the whole book, and after reading 30 pages, he will finish reading it all. How many pages does this storybook have?
小明看一本故事书，已经看了全书的40%，再看30页就全部看完，这本故事书共多少页？
<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (2/5)</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">30 / (3/5)</gadget>
<output>50</output>

<result>50</result>