book has 120 pages. I read 20% of the whole book on the first day, and 3/4 of the whole book on the second day. How many percent have I left?
一本书有120页，第一天看了全书的20%，第二天看了全书的(3/4)，还有百分之几没看？
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">(1/5) + (3/4)</gadget>
<output>19/20 = around 0.95</output>

<gadget id="calculator">1 - (19/20)</gadget>
<output>1/20 = around 0.05</output>

<result>1/20 = around 0.05</result>