If 60% of 1 ton of coal is used up, how many tons are left?
1吨煤用去60%，还剩多少吨．
<gadget id="calculator">60 / 100</gadget>
<output>3/5 = around 0.6</output>

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

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

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