Plan to burn 15 tons of coal, and actually burn 13 tons of coal, saving coal ((())/(())).
计划烧煤15吨，实际烧煤13吨，节约用煤((())/(()))．
<gadget id="calculator">15 - 13</gadget>
<output>2</output>

<gadget id="calculator">2 / 15</gadget>
<output>2/15 = around 0.133333</output>

<result>2/15 = around 0.133333</result>