On Arbor Day, the school distributes a batch of saplings to students in grades 4-6 to plant. If the fourth grade students complete it alone, each person will plant 12 trees on average; if the fifth grade students complete it alone, each person will plant 20 trees on average; The sixth grade students completed it alone, with an average of 30 plants per person. Now all the students in grades 4-6 are going to plant, with an average of how many trees are planted per person.
植树节那天，学校把一批树苗分给4-6年级学生去植，如果由四年级学生单独完成，平均每人植12棵；如果由五年级学生单独完成，平均每人植20棵；如果六年级学生单独完成，平均每人植30棵．现由4-6年级三个年级学生都去植，平均每人植几棵．
<gadget id="calculator">600 / 12</gadget>
<output>50</output>

<gadget id="calculator">600 / 20</gadget>
<output>30</output>

<gadget id="calculator">600 / 30</gadget>
<output>20</output>

<gadget id="calculator">50 + 30 + 20</gadget>
<output>100</output>

<gadget id="calculator">600 / 100</gadget>
<output>6</output>

<result>6</result>