To calculate the average speed of a bus in miles per minute when it travels at a speed of X miles in Y minutes, you divide the total distance traveled (X miles) by the total time taken (Y minutes).
Average speed (in miles per minute) = X miles / Y minutes
For example, if a bus travels 50 miles in 120 minutes:
Average speed = 50 miles / 120 minutes = 0.4167 miles per minute
Please note that this calculation assumes a constant speed throughout the entire duration of the journey. In real-world scenarios, a bus's speed may vary depending on factors such as traffic, road conditions, and stops, which would affect the average speed.