Elena's bus runs every 20 minutes. If she arrives at her bus stop at a random time, what is the probability that she will have to wait at least 5 minutes for the bus if it is running on schedule?

We try to represent the data in segments from 0 to 20.

The length of the line segment along the number line from 0 to 5 is 5 - 0 = 5 units. The length of the line segment along the number line from 20 to 5 is 20 - 5 = 15 units. If you were to randomly throw a dart on this number line, then the probability of landing in the shaded region is 15/20 = 3/4 or 75%