If a number is reduced by 20%, it is 64. What is the number?
一个数减少它的20%后是64，这个数是多少．
<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">64 / (4/5)</gadget>
<output>80</output>

<result>80</result>