After drinking 20% of a glass of milk, fill it up with water, drink 40% again, and then fill it up again. How much milk is in the glass at this time?
一杯牛奶，喝去20%以后，加满水，再喝去40%，再加满水，这时杯中牛奶占多少
<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">40 / 100</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">(4/5) * (3/5)</gadget>
<output>12/25 = around 0.48</output>

<result>12/25 = around 0.48</result>