A piece of iron wire is 7 meters long, if (4/7) of it is used up, how many meters are left?
一根铁丝长7米，用去了它的(4/7)，还剩多少米．
<gadget id="calculator">4 / 7</gadget>
<output>4/7 = around 0.571429</output>

<gadget id="calculator">1 - (4/7)</gadget>
<output>3/7 = around 0.428571</output>

<gadget id="calculator">7 * (3/7)</gadget>
<output>3</output>

<result>3</result>