The sixth grade students participated in the tree planting activity. The school prepared three kinds of trees: poplar, willow and pine, and each person planted at least one kind. It is known that 80% of the students who planted poplars and 80% of the students who planted willows in the whole grade 90%, students who plant pine trees account for 70% of the whole grade, so what percentage of the whole grade are students who plant three kinds of trees?
六年级同学参加植树活动，学校准备了杨树、柳树、松树三种树，每人至少植一种，已知种杨树的同学占全年级的80%，种柳树的同学占了全年级的90%，种松树的同学占了全年级的70%，那么三种树的同学占了全年级的百分之几？
<gadget id="calculator">80 / 100</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">1 - (4/5)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">90 / 100</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">1 - (9/10)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">70 / 100</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">1 - (7/10)</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">1 - (1/5) - (1/10) - (3/10)</gadget>
<output>2/5 = around 0.4</output>

<result>2/5 = around 0.4</result>