A glass of milk, drink (1/5) and then fill up with water, drink (1/5) and then fill up with water, what is the concentration of milk at this time?
一杯牛奶，喝去(1/5)再加满水，又喝去(1/5)后再加满水，此时牛奶的浓度是多少．
<gadget id="calculator">1 / 5</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) * (1/5)</gadget>
<output>4/25 = around 0.16</output>

<gadget id="calculator">(1/5) + (4/25)</gadget>
<output>9/25 = around 0.36</output>

<gadget id="calculator">1 - (9/25)</gadget>
<output>16/25 = around 0.64</output>

<gadget id="calculator">(16/25) / 1</gadget>
<output>16/25 = around 0.64</output>

<result>16/25 = around 0.64</result>