John's favorite exercise machine is a stair climber. On the "random" setting, it changes speeds at regular intervals, so the total number of simulated "floors" he climbs varies
from session to session. John also exercises for different lengths of time each session.
He decides to explore the relationship between how long he works out on the stair
climber (in minutes) and the number of floors it tells him that he has climbed. John
records minutes of climbing time and number of floors climbed for six exercise sessions.
Computer output and a residual plot from a linear regression analysis of the data are
shown below.