A rope is 4 meters long, (1/4) is used up, and ((())/(())) is left, how many meters are left.
一条绳子长4米，用去(1/4)，还剩((())/(()))，还剩多少米．
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 - (1/4)</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">4 * (3/4)</gadget>
<output>3</output>

<result>3</result>