Final answer:
The mean change in elevation per mile is 55 feet.
Step-by-step explanation:
To find the mean change in elevation per mile, we need to calculate the total change in elevation and divide it by the total miles driven.
The total change in elevation is the difference between the elevation of your friend's house (680 feet) and your house (240 feet): 680 - 240 = 440 feet.
The total distance driven is 8 miles.
To find the mean change in elevation per mile, divide the total change in elevation by the total miles driven: 440 feet / 8 miles = 55 feet per mile.
Therefore, the mean change in elevation per mile is 55 feet per mile.