Xiaogang has to do 50 math problems, and he has done 40. What percentage is left?
小刚要做50道口算题，已经做了40道，还剩百分之几没有做？
<gadget id="calculator">50 - 40</gadget>
<output>10</output>

<gadget id="calculator">10 / 50</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">100 / 100</gadget>
<output>1</output>

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

<result>1/5 = around 0.2</result>