posted by Bob .
An escalator moves down at the rate of 60 steps per minute. Alan can walk fast up ordinary steps at the rate of 80 steps per minute. There are 50 steps from one level to another. Alan decides to walk fast up the down escalator. How long will it take him to go up one level?
Up rate on the down escalator = 80 - 60 = 20 step/min. Time spent going up one level = 50/20 =2.5 minutes