glass of milk, after drinking (1/5), fill it up with water, and drink (1/5) again, then fill it up with water, what is the original milk in the glass
一杯奶，喝了(1/5)后用水加满，又喝了(1/5)后，用水加满，这时杯子中的奶是原来的多少
<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 - (1/5) - (4/25)</gadget>
<output>16/25 = around 0.64</output>

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