After drinking 20% of a full glass of pure milk, fill it up with water and stir well, then drink 60% of it. At this time, the pure milk in the glass is the volume of the glass.
一满杯纯牛奶，喝去20%后，加满水搅匀，再喝去60%，这时杯中的纯牛奶是杯子容积的多少．
<gadget id="calculator">20 / 100</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">60 / 100</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">1 - (3/5)</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(4/5) * (2/5)</gadget>
<output>8/25 = around 0.32</output>

<result>8/25 = around 0.32</result>