The subway 1.8km, with a speed of 54km/h, how many minutes does it take to solve the math problem?
Speed 54 km/h = 15 m/s
Then the distance traveled by the train 1 min in 20 seconds is 15*80= 1200m.
Since the bridge length is 1 100m, the train will leave the bridge after traveling 1200m, so it can be concluded that the train length is1200-1100 =100m.