There are 40 poplar trees planted every 2 meters around a circular pool. What is the circumference of the pool in meters?
一个圆形水池周围每隔2米栽一棵杨树，共栽了40棵，水池的周长是多少米．
<gadget id="calculator">40 * 2</gadget>
<output>80</output>

<result>80</result>