According to Google Maps, it's 241 miles from Ann Arbor to Chicago. If Kevin made this trip in 4 hours, what was his average rate of travel during the trip?
If Kevin travelled 241 miles in 4 hours, his average rate of travel was
Look at a graph of Kevin's position (measured in miles from Ann Arbor) vs. time (measured in hours since the start of the trip). We don't know Kevin's exact position during most of the trip, since we don't know how fast he was driving, but we know his position was 0 miles at the beginning of the trip and 241 miles at the end of the trip:
The distance Kevin traveled is equal to his ending position minus his starting position, which can be seen on the vertical axis:
The time the trip took can be seen on the horizontal axis:
When we take the quotient
we're finding the slope of the line between two points: