(7/10) tons of coal are used up (1/2), how many tons are left.
(7/10)吨煤用去(1/2)，还剩多少吨．
<gadget id="calculator">7 / 10</gadget>
<output>7/10 = around 0.7</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">(7/10) * (1/2)</gadget>
<output>7/20 = around 0.35</output>

<result>7/20 = around 0.35</result>