Li Hua rides a bicycle from A to B, traveling 400 meters per minute, and returning immediately after arriving at B, traveling 600 meters per minute, what is Li Hua's average round trip speed?
李华骑车由甲地到乙地，每分钟行400米，到达乙地后立即返回，每分钟行600米，求李华往返的平均速度？
<result>480</result>