A rope 2 meters long, first use up (1/3), then use up (1/3) meters, how many meters are left.
一根长2米的绳子，先用去(1/3)，再用去(1/3)米，还剩下多少米．
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 - (1/3)</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">2 * (2/3)</gadget>
<output>4/3 = around 1.333333</output>

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

<result>1</result>