4: 20% = x: 0.5.
4：20%=x：0.5．
<gadget id="calculator">4 * 0.5</gadget>
<output>2</output>

<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">2 / (1/5)</gadget>
<output>10</output>

<result>10</result>