A glass of 20% sugar water is poured out and then filled with water. What is the current concentration?
一杯浓度为20%的糖水，倒出20%后又兑满水，现在浓度是多少
<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">(4/5) / 1</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">1 * (1/5) * (4/5)</gadget>
<output>4/25 = around 0.16</output>

<result>4/25 = around 0.16</result>