A full glass of water, the first time I drank (2/5) cup, and the second time I drank (1/5) cup, how much more water do I need to fill the glass again?
一满杯水，第一次喝掉了(2/5)杯，第二次喝掉了(1/5)杯，需要再倒入多少水又能把杯子灌满？
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(2/5) + (1/5)</gadget>
<output>3/5 = around 0.6</output>

<result>3/5 = around 0.6</result>