There is a pile of coal, 20% of which was used for the first time, and 2 tons were used for the second time, and 3.4 tons were used for the two times. How many tons does this pile of coal weigh?
有一堆煤，第一次用去20%，第二次又用去2吨，两次一共用去3.4吨．这堆煤重多少吨？
<gadget id="calculator">3.4 - 2</gadget>
<output>1.4</output>

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

<gadget id="calculator">1.4 / (1/5)</gadget>
<output>7</output>

<result>7</result>