I just wanted to know how to find average speed without knowing the distance. I know average speed is defined as total distance / change in time but what would you do a person travels to a friend's house and when he is halfway there, he figures out that he has been averaging 30 mph. He drives the last half of the trip at 60 mph. What is Joe’s average speed for the entire journey? I figured it was just 30 + 60 divided by 2 but apparently i am wrong. anyone can help?