A pile of coal weighs 20 tons. Vehicle A transports (1/5) of it, and vehicle B transports (2/7) of it. What fraction of the coal is left?
一堆煤重20吨，甲车运走了它的(1/5)，乙车运走了它的(2/7)，还剩下这堆煤的几分之几？
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">1 - (1/5) - (2/7)</gadget>
<output>18/35 = around 0.514286</output>

<result>18/35 = around 0.514286</result>