The school held tree-planting activities. The number of trees planted by third-grade students accounted for (2/7) of the total number of trees planted in the school, and the number of trees planted by fourth-grade students accounted for (4/7) of the total. What percentage of the total number of trees planted by students in other grades?
学校举行植树活动，三年级学生植树棵数占全校植树总棵数的(2/7)，四年级学生植树棵数占总数的(4/7)．其它年级学生植树棵数占总数的几分之几？
<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>