A pile of coal, 60% of it is used, and there are 24 tons left; if 50% of it is used, how many tons are left.
一堆煤，用去它的60%，还剩下24吨；若用去它的50%，则剩下多少吨．
<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">24 / (2/5)</gadget>
<output>60</output>

<gadget id="calculator">50 / 100</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">60 * (1/2)</gadget>
<output>30</output>

<result>30</result>