Xiaojun reads a story book and reads 25 pages every day. After 4 days, he reads exactly half of the book. How many pages does this storybook have?
小军看一本故事书，每天看25页，看了4天后正好看了这本书的一半．这本故事书一共有多少页？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">4 / (1/2)</gadget>
<output>8</output>

<gadget id="calculator">25 * 8</gadget>
<output>200</output>

<result>200</result>