A glass of water, after drinking (1/7) for the first time, and (3/7) for the second time, there is still ((())/(())) of this glass of water.
一杯水，第一次喝了(1/7)，第二次喝了(3/7)，还剩这杯水的((())/(()))．
<gadget id="calculator">1 / 7</gadget>
<output>1/7 = around 0.142857</output>

<gadget id="calculator">3 / 7</gadget>
<output>3/7 = around 0.428571</output>

<gadget id="calculator">1 - (1/7) - (3/7)</gadget>
<output>3/7 = around 0.428571</output>

<result>3/7 = around 0.428571</result>