A glass of milk, the first time I drank it (1/5), the second time I drank it (2/5), what percentage is left?
一杯牛奶，第一次喝了它的(1/5)，第二次喝了它的(2/5)，还剩几分之几没有喝？
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

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

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