On Arbor Day, the teachers and students went to plant trees, and the students were divided into 4 groups on average, with 20 people in each group, and 320 trees were to be planted. How many trees were planted per person on average?
植树节老师同学们去植树，把同学们平均分成4组，每组20人，要植树320棵，平均每人植树多少棵？
<gadget id="calculator">20 * 4</gadget>
<output>80</output>

<gadget id="calculator">320 / 80</gadget>
<output>4</output>

<result>4</result>