How to calculate the average speed of an object on a graph

When you are given a position and time graph about an object's movement, you are likely to be asked what was the average velocity of the object throughout the trip. If the object's speed is constant, then the average speed is the change of position divided by time. If the speed isn't constant, then each time the speed changes, add all of the different amounts of position change and changes in time together, then divide the total amount of position change by the total amount time change.