For a barrel of oil, the whole barrel (3/7) is used for the first time, and the whole barrel (1/7) is used for the second time, what percentage is shared between the two times?
一桶油，第一次用去全桶的(3/7)，第二次用去全桶的(1/7)，两次共用去几分之几？
<gadget id="calculator">3 / 7</gadget>
<output>3/7 = around 0.428571</output>

<gadget id="calculator">1 / 7</gadget>
<output>1/7 = around 0.142857</output>

<gadget id="calculator">(3/7) + (1/7)</gadget>
<output>4/7 = around 0.571429</output>

<result>4/7 = around 0.571429</result>