After drinking 20% of a cup of pure milk, fill it up with water and stir well, and then drink 50%, how much of the cup's capacity is the pure milk in the cup
一杯纯牛奶喝去20%后加满水搅匀，再喝去50%，这时杯中纯牛奶占杯子容量的多少
<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">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(4/5) * (1/2)</gadget>
<output>2/5 = around 0.4</output>

<result>2/5 = around 0.4</result>