Xiaoqiang reads a storybook and reads 20 pages every day. After 5 days, there are still (1/5) of the whole book left unread. How many pages are there in this storybook?
小强看一本故事书，每天看20页，5天后还剩下全书的(1/5)没看，这本故事书有多少页．
<gadget id="calculator">20 * 5</gadget>
<output>100</output>

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

<gadget id="calculator">1 - (1/5)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">100 / (4/5)</gadget>
<output>125</output>

<result>125</result>