A rope 2 meters long, use up (1/4), how many meters are left.
一根长2米的绳子，用去(1/4)，还剩多少米．
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">2 * (1/4)</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">2 - (1/2)</gadget>
<output>3/2 = around 1.5</output>

<result>3/2 = around 1.5</result>