Xiaodong reads a book and reads 20 pages a day. After 4 days, 3/8 of the book has not been read. How many pages does this book have?
小东看一本书，每天看20页，4天后还剩全书的(3/8)没有看，这本书共有多少页？
<gadget id="calculator">20 * 4</gadget>
<output>80</output>

<gadget id="calculator">3 / 8</gadget>
<output>3/8 = around 0.375</output>

<gadget id="calculator">1 - (3/8)</gadget>
<output>5/8 = around 0.625</output>

<gadget id="calculator">80 / (5/8)</gadget>
<output>128</output>

<result>128</result>