Li Village uses a harvester to harvest wheat. On the first day, the harvesting task of the whole village (1/4) is completed, and on the second day, the harvesting task of the whole village (2/5) is completed. On the third day, the whole village is less than the sum of the previous two days (3/10), what percentage of the village's tasks were completed on the third day.
李村用收割机收割小麦，第一天完成全村(1/4)的收割任务，第二天完成全村(2/5)的收割任务，第三天比前两天的总和少全村(3/10)，第三天完成全村任务的几分之几．
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(1/4) + (2/5)</gadget>
<output>13/20 = around 0.65</output>

<gadget id="calculator">3 / 10</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">(13/20) - (3/10)</gadget>
<output>7/20 = around 0.35</output>

<result>7/20 = around 0.35</result>