Dongdong reads a book. If he reads 50 pages a day, he can finish it on schedule. If he reads 10 more pages a day, he can finish it 10 days in advance. How many pages does this book have?
东东读一本书，如果每天读50页，那么可按期读完，如果他每天多读10页，那么可提前10天读完．这本书一共有多少页？
<gadget id="calculator">10 * 50</gadget>
<output>500</output>

<gadget id="calculator">10 * 10</gadget>
<output>100</output>

<gadget id="calculator">500 + 100</gadget>
<output>600</output>

<gadget id="calculator">10 - 50</gadget>
<output>-40</output>

<gadget id="calculator">50 + (-40)</gadget>
<output>10</output>

<gadget id="calculator">600 / 10</gadget>
<output>60</output>

<gadget id="calculator">50 * 60</gadget>
<output>3_000</output>

<result>3_000</result>