watermelon, Xiao Ming ate (2/5) of it, and Xiao Hua ate (1/5) of it, how much of the watermelon did they eat? What fraction is left?
一个西瓜，小明吃了它的(2/5)，小华吃了它的(1/5)，他们一共吃了这个西瓜的几分之几？还剩下几分之几？
<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>

<gadget id="calculator">1 - (3/5)</gadget>
<output>2/5 = around 0.4</output>

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