A poplar tree is planted every 2 meters around a circular pool. A total of 20 poplar trees are planted. What is the circumference of the pool in meters?
一个圆形水池周围每隔2米栽一颗杨树，共栽20棵，水池的周长是多少米？
<gadget id="calculator">20 * 2</gadget>
<output>40</output>

<result>40</result>