Arithmetic and weighted means

The arithmetic mean is total divided by count. For frequency data, weight each value or class midpoint by its frequency. Grouped means are estimates because midpoints replace unknown individual values. Adding c to all observations adds c to the mean; multiplying by b multiplies the mean by b. The mean uses every value and is sensitive to extreme observations. Always retain units and round only the final result. mean = ∑x/n; weighted mean = ∑fx/∑f