The 20 kilograms poured out of a barrel of oil just account for (5/7) of the whole barrel of oil, how many kilograms of this barrel of oil are left.
一桶油倒出的20千克，恰好占全桶油的(5/7)，这桶油还剩下多少千克．
<gadget id="calculator">5 / 7</gadget>
<output>5/7 = around 0.714286</output>

<gadget id="calculator">20 / (5/7)</gadget>
<output>28</output>

<gadget id="calculator">28 - 20</gadget>
<output>8</output>

<result>8</result>