Lets say you have a distance x = 1 mile. If you run that 1 mile and it takes you 10 minutes, you had a speed of 0.1 miles per minute. Then you run the mile again and it only takes you 8 minutes this time. Now your speed is 0.125 miles per minute. You speed has increased from 0.1 to 0.125 miles per minute. If you want to decrease the time it takes to travel across a distance, then you must increase your speed.
