Mechanics and Logic
A passenger can walk up a stationary escalator in 3 minutes. If this very same escalator is moving, however, and the passenger is still walking upwards with the same speed, he will be at the top in 2 minutes. Will he be able to walk up an escalator which is moving at the same speed downwards (i.e. in the opposite direction to the passenger's direction of motion)? If so, then how long would it take him to reach the top?