barrel of oil is used (3/7), and the remaining is much more than what is used.
一桶油用去(3/7)，剩下的比用去的多多少．
<gadget id="calculator">3 / 7</gadget>
<output>3/7 = around 0.428571</output>

<gadget id="calculator">1 - (3/7) - (3/7)</gadget>
<output>1/7 = around 0.142857</output>

<gadget id="calculator">(1/7) / (3/7)</gadget>
<output>1/3 = around 0.333333</output>

<result>1/3 = around 0.333333</result>