Sun Gang has a story book. He read 40% of the whole book in the first month, and the remaining 60% in the second month. At this time, there are 120 pages left. How many pages does this book have?
孙刚有一本故事书，第一个月读了全书的40%，第二个月读了余下的60%，这时还剩下120页没有读，这本书共有多少页？
<gadget id="calculator">60 / 100</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">1 - (3/5)</gadget>
<output>2/5 = around 0.4</output>

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

<gadget id="calculator">1 - (2/5)</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">120 / (2/5) / (3/5)</gadget>
<output>500</output>

<result>500</result>