## Elementary Statistics (12th Edition)

The mean can be counted by summing all the data and dividing it by the number of data. Also, at each age group we take the midrange of the group to calculate. The midranges: 50-59:54.5, 60-69:64.5, 70-79:74.5, 80-89:84.5, 90-99:94.5, 100-109:104.5, 110-119:114.5, 120-129:124.5. The mean: $\frac{54.5\cdot4+64.5\cdot10+74.5\cdot25+84.5\cdot43+94.5\cdot26+104.5\cdot8+114.5\cdot3+124.5\cdot2}{121}=84.67$. The actual mean is more accurate, and a bit less than the one we've calculated.