Easy Understandable Approach


The speed of both the trains is 100 mph, and both are moving towards each other. So, Total time taken by the trains to collide will be 1 hr( As the tunnel is 200 miles long). The bee does not stop flying until the trains collide. Therefore, The total time for which the bee will travel will be equal to the: speed of the bee(1000 mph) * time required for the collision of trains(1 hr).