Xiao Ming reads a book. He reads 30% of the whole book on the first day, and 30 pages on the second day. There is still (1/2) of the whole book left. How many pages does this book have?
小明看一本书，第一天看了全书的30%，第二天看了30页，还剩全书的(1/2)没看，这本书共有多少页？
<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 - (3/10) - (1/2)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">30 / (1/5)</gadget>
<output>150</output>

<result>150</result>