Xiaoying reads a story book. On the first day, she read 40% of the whole book. On the first day, she read 10 pages less than on the second day, so she just finished it. How many pages does this storybook have?
小莹看一本故事书，第一天看了全书的40%，第一天比第二天少看了10页，正好看完．这本故事书有多少页？
<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (2/5) - (2/5)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">10 / (1/5)</gadget>
<output>50</output>

<result>50</result>