(4/5) is used for a pile of coal, which is exactly (1/5) ton. How many tons is this pile of coal originally? What is the column
一堆煤用去(4/5)，正好是(1/5)吨，这堆煤原来是多少吨？列式是多少
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">(1/5) / (4/5)</gadget>
<output>1/4 = around 0.25</output>

<result>1/4 = around 0.25</result>