The first time I drank a glass of water (1/2), the second time I drank the remaining water (1/2), how much water is left in this glass of water
我第一次喝一杯水的(1/2)，第二次喝剩下水的(1/2)，这杯水还剩多少
<gadget id="calculator">1 / 2</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">(1/2) * (1/2)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 - (1/2) - (1/4)</gadget>
<output>1/4 = around 0.25</output>

<result>1/4 = around 0.25</result>