A story book, I read (1/5) of the whole book on the first day, and 30% of the whole book on the second day, and there are 120 pages left. How many pages are in this book?
一本故事书，第一天看了全书的(1/5)，第二天看了全书的30%，还剩下120页没看，这本书多少页？
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">1 - (1/5) - (3/10)</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">120 / (1/2)</gadget>
<output>240</output>

<result>240</result>