A piece of wire, use up (2/5) of the full length, and there are 30 meters left, how many meters are used, and there is still ((())/(())).
一段电线，用去全长的(2/5)，还剩30米，用去了多少米，还剩下((())/(()))．
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (2/5)</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">30 / (3/5)</gadget>
<output>50</output>

<gadget id="calculator">50 - 30</gadget>
<output>20</output>

<result>20</result>