A pile of yellow sand transports away 20% of it every day, and how much is left after transporting for 3 days.
一堆黄沙每天运走它的20%，运了3天后还剩多少没运走．
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/5) * 3</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">1 - (3/5)</gadget>
<output>2/5 = around 0.4</output>

<result>2/5 = around 0.4</result>