All SAT GuidesStudy Guide
One-Variable Data: Mean, Median and Spread
Summarize one set of measurements using a center and a measure of spread. Mean uses every value; median is the middle of the ordered data.
Key Rules
- Mean equals the sum divided by the number of observations.
- Order the observations before finding the median; with an even count, average the two middle values.
- A large outlier can strongly change the mean while leaving the median unchanged.
Common Mistakes to Avoid
- Finding the middle of an unordered list.
- Averaging group averages without accounting for different group sizes.
SAT Strategy Tips
- →For a frequency table, use each value’s frequency when adding and counting.
- →Distinguish the center of a distribution from how widely the values vary.
Example Question
For the data 2, 3, 3, 8, 9, what are the mean and median?