7th Grade · Statistics & Probability
Measure of Center
7.SP.B.4
Definition
Values that represent the middle of a data set. Mean = average (sum ÷ count). Median = middle value when ordered. Choose based on whether outliers are present.
Examples
- {3,5,7,8,9,10,12}: mean ≈ 7.7, median = 8.
- House prices $150K,$160K,$170K,$1,000K: mean $370K is pulled up; median $165K is the better center.
Key rule
Use mean when data is symmetric with no outliers; use median when outliers are present.
Memory hook
Mean gets pulled by outliers; median doesn't.