Xiaofang reads a book, read the whole book (3/10) on the first day, read 81 pages on the second day, and left 40% of the book. How many pages does this book have?
小芳看一本书，第一天看了全书的(3/10)，第二天看了81页，还剩全书的40%没看．这本书一共有多少页？
<gadget id="calculator">3 / 10</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (3/10) - (2/5)</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">81 / (3/10)</gadget>
<output>270</output>

<result>270</result>