mean, , number of seconds it takes to open the aspirin bottle. 4) According to the Bureau of the Census, the mean annual income of government employees is $35,000. There is some doubt that this mean is representative of incomes of government employees living in the San Francisco Bay area. Based on a sample of 49 government employees yielding a mean of $35,600 and a standard deviation of $1400, at the .05 level of significance, test whether there is sufficient evidence to conclude that the mean annual income of government employees living in the Bay area is different than the national average