What was the age distribution of prehistoric Native Americans? Extensive anthropological studies in the southwestern United States gave the following information abou prehistoric extended family group of 85 members on what is now a Native American reservation. For this community, estimate the mean age expressed in years, the sa variance, and the sample standard deviation. For the class 31 and over, use 35.5 as the class midpoint. (Round your answers to one decimal place.) Age range (years) 1-10 11-20 21-30 31 and over Number of individuals 37 24 16 8 X = S=