A 10-meter-long rope is used for the first time (1/5), how many meters is left?
一根10米长的绳子，第一次用去了(1/5)，还剩多少米．
<gadget id="calculator">1 / 5</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">10 * (4/5)</gadget>
<output>8</output>

<result>8</result>