After 20% of a sum of money is used up, there is still 20 yuan left, how much is the money.
一笔钱用去20%后，还剩20元，这笔钱有多少元．
<gadget id="calculator">20 / 100</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">20 / (4/5)</gadget>
<output>25</output>

<result>25</result>