Solution :
Given :
X = homicide rate (homicides per 100,00 population)
n = 12 = metropolitan areas
Area              X (homicides per 100,000 population)
Mesa, AZ Â Â Â Â Â Â Â Â Â 4.1
Seattle, WA Â Â Â Â Â Â Â 3.8
Portland, OR (tie) Â Â Â 3.4
New York, NY(tie) Â Â 3.4
Virginia beach, VA Â 3.3
San Jose, CA Â Â Â Â Â 3.1
EI, Paso, TX Â Â Â Â Â Â 2.6
Austin, TX Â Â Â Â Â Â Â Â 2.6
San Diago, CA Â Â Â Â 2.4
Suffolk County     2.2
Montgomery, MD Â Â 2.0
Fairfax, VA Â Â Â Â Â Â Â 1.7
Therefore, the mean of X = [tex]$\bar X = \frac{\sum X_i}{n}$[/tex]
                      [tex]$=\frac{34.9}{12}$[/tex]
                     = 2.9
Therefore, the mean of homicide rater in the 12 metropolitan areas is 2.9 homicide per 100,000 population.