1 ton of coal, (1/5) ton is used for the first time, and (2/5) ton is used for the second time, how many tons are left?
1吨煤，第一次用去(1/5)吨，第二次用去(2/5)吨，还剩下多少吨？
<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">(1/5) + (2/5)</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>