A book, I read (1/5) on the first day, and the rest (1/2) on the second day, and I didn’t read the rest of the book.
一本书，第一天看了(1/5)，第二天看了余下的(1/2)，还剩下全书的多少没看．
<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">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(4/5) * (1/2)</gadget>
<output>2/5 = around 0.4</output>

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

<result>2/5 = around 0.4</result>