In a mountaineering competition, Xiao Gang walked 40 meters per minute when going up the mountain, 18 minutes to reach the top of the mountain, and then walked down the mountain by the same route, walking 60 meters per minute. What is the average speed of Xiaogang's round trip?

Answer and analysis:

Distance = speed * time, average speed = total distance/total time. The distance up and down the mountain is equal.

Uphill (downhill) distance =40* 18=720 (m)

Downhill time =720/60= 12 (minutes)

Requirements: average speed = 720 * 2/(18+12) = 48 (m/min).