A glass of water, drank (2/4) and poured (1/4), how much is left now?
一杯水，喝了(2/4)又倒进了(1/4)，现在还有几分之几？
<gadget id="calculator">2 / 4</gadget>
<output>1/2 = around 0.5</output>

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

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(1/2) + (1/4)</gadget>
<output>3/4 = around 0.75</output>

<result>3/4 = around 0.75</result>