Use a tractor to plow the land, plow the land on the first day (1/5), plow the land on the second day (2/7), plow all the land on the third day, and plow the land on the third day How much?
用拖拉机耕地，第一天耕这块地的(1/5)，第二天耕这块地的(2/7)，第三天全部耕完，第三天耕了这块地的几分之几？
<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">(1/5) + (2/7)</gadget>
<output>17/35 = around 0.485714</output>

<gadget id="calculator">1 - (17/35)</gadget>
<output>18/35 = around 0.514286</output>

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