Among 25 randomly selected runners in the Boston Marathon, the mean difference in heart rate
measured at the beginning and end of the race was 39 beats per minute, and the standard deviation
was 15.2 beats per minute. Differences were computed by subtracting the heart rate at the beginning of
the race from the heart rate at the end of the race.
Is there a statistically significant difference in mean heart rates measured before and after the Boston
Marathon? Use a = .05.