A piece of iron wire is 20 meters long, 20% of the total length is used up, how many meters are used up?
一根铁丝长20米，用去全长的20%，用去了多少米．
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">20 * (1/5)</gadget>
<output>4</output>

<result>4</result>