There are 2 tons of corn in the warehouse, the first time it is transported away (2/7), and the second time it is transported away (4/7), how much of all the corn is left
仓库里有玉米2吨，第一次运走它的(2/7)，第二次运走它的(4/7)，还剩全部玉米的多少
<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

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

<gadget id="calculator">1 - (2/7) - (4/7)</gadget>
<output>1/7 = around 0.142857</output>

<result>1/7 = around 0.142857</result>