A glass of milk has already been drunk (2/5), what is left is how much is left.
一杯牛奶，已经喝了(2/5)，喝了的是剩下的多少．
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (2/5)</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">(2/5) / (3/5)</gadget>
<output>2/3 = around 0.666667</output>

<result>2/3 = around 0.666667</result>