When Xiaoguang reads a story book, the ratio of what he has read to the rest is 1:4. If he reads another 20 pages, he has read 1/3 of the whole book. How many pages does this book have?
小光看一本故事书，已看的与剩下的比是1：4，如果他再看20页，就看了整书的(1/3)，这本书有多少页？
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 + 4</gadget>
<output>5</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/3) - (1/5)</gadget>
<output>2/15 = around 0.133333</output>

<gadget id="calculator">20 / (2/15)</gadget>
<output>150</output>

<result>150</result>