pile of coal burned 20% of the total in the first week, 240 tons in the second week, and exactly half of the total in two weeks. How many tons did this pile of coal have?
一堆煤，第一周烧了总数的20%，第二周烧了240吨，两周正好烧了总数的一半，这堆煤原有多少吨？
<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">240 / (3/10)</gadget>
<output>800</output>

<result>800</result>