A pile of sand has been used up (1/5), and there are still 84 tons left. How many tons is this pile of sand originally?
一堆沙子用去了(1/5)，还剩下84吨，这堆沙子原来有多少吨？
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (1/5)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">84 / (4/5)</gadget>
<output>105</output>

<result>105</result>