A pile of coal, its (1/7) was transported away on the first day, and its (4/7) was transported away on the second day, what fraction of the coal is left untransported?
一堆煤，第一天运走它的(1/7)，第二天运走了它的(4/7)，还剩下这堆煤的几分之几没有运？
<gadget id="calculator">1 / 7</gadget>
<output>1/7 = around 0.142857</output>

<gadget id="calculator">4 / 7</gadget>
<output>4/7 = around 0.571429</output>

<gadget id="calculator">1 - (1/7) - (4/7)</gadget>
<output>2/7 = around 0.285714</output>

<result>2/7 = around 0.285714</result>