There is a pile of coal, 20% of which was used in the first week, 12 tons were used in the second week, and 50% of the pile of coal was used up in two weeks. How many tons is this pile of coal?
有一堆煤，第一周用去了20%，第二周用去了12吨，两周共用去了这堆煤的50%．这堆煤一共有多少吨？
<gadget id="calculator">50 / 100</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/2) - (1/5)</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">12 / (3/10)</gadget>
<output>40</output>

<result>40</result>