The school organizes students to plant trees. The number of trees planted by Class 51 and Class 52 accounts for (2/5) of the total number of the whole grade, among which the number of trees planted by Class 51 accounts for (1/6) of the whole grade, and the number of trees planted by Class 52 accounts for the total number of trees planted in the whole year. What fraction of the number of trees?
学校组织学生植树，五一班和五二班植树棵数共占全年级总数的(2/5)，其中五一班植树占全年级的(1/6)，五二班植树占全年级总棵数的几分之几？
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">(2/5) - (1/6)</gadget>
<output>7/30 = around 0.233333</output>

<result>7/30 = around 0.233333</result>