A pile of coal (4/5) tons, (1/2) is used for the first time, and the remaining (1/2) is used for the second time, how many tons are left.
一堆煤(4/5)吨，第一次用去(1/2)，第二次用去余下的(1/2)，还剩多少吨．
<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

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

<gadget id="calculator">(4/5) * (1/2) * (1/2)</gadget>
<output>1/5 = around 0.2</output>

<result>1/5 = around 0.2</result>