The school carried out environmental protection activities. Four groups collected a total of 640 waste batteries. Each group had 8 people. How many waste batteries did they collect on average?
学校开展环保活动，有四个小组共收集640节废电池，每个小组有8人，他们平均每人收集废电池多少节？
<gadget id="calculator">640 / 4 / 8</gadget>
<output>20</output>

<result>20</result>