The mass of a pile of coal is equal to the weight of the pile of coal (1/5) plus (2/5) tons, how many tons does the pile of coal weigh?
一堆煤的质量等于这堆煤重的(1/5)加上(2/5)吨，这堆煤重多少吨．
<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">1 - (1/5)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">(2/5) / (4/5)</gadget>
<output>1/2 = around 0.5</output>

<result>1/2 = around 0.5</result>