Final answer:
To arrive on time after a 6-minute late departure, the train must travel at a new average speed of 125km/hr to cover the 300km journey, given that it was originally scheduled to travel at 120km/hr.
Step-by-step explanation:
To find out the new average speed at which the train must travel to cover a journey of 300km to arrive on time after leaving 6 minutes late, we first calculate the original time it would take at an average speed of 120km/hr.
Time = Distance ÷ Speed = 300km ÷ 120km/hr = 2.5 hours.
Since the train leaves 6 minutes late, the time it has to complete the trip is reduced to 2.5 hours - 6 minutes (which is 0.1 hours), so it has 2.4 hours to complete the journey.
We can now find the new average speed by dividing the total distance by the new time:
New average speed = Distance ÷ New time = 300km ÷ 2.4 hours = 125km/hr.
Therefore, the train must travel at an average speed of 125km/hr to make up for the lost time.