Mean, Median, Mode, and Range

Mean (average): Add all values and divide by the count. [formula] Median: The middle value when data is ordered. For an even number of values, average the two middle values. Mode: The most frequent value. A data set can have no mode, one mode, or multiple modes.

Example: Find the mean, median, and mode of: 3, 7, 7, 12, 15

Range = text{Maximum} - text{Minimum} The range measures spread but is sensitive to outliers (extreme values). Effect of outliers: - Mean: strongly affected (pulled toward the outlier) - Median: resistant (barely changes) - Mode: not affected The SAT loves asking which measure is most affected by an outlier — it's always the mean.

Example: Data: 10, 12, 13, 14, 50. How does removing 50 affect the mean and median?

Shortcut for finding missing values: If the mean of n numbers is bar{x}, the total is n times bar{x}. So if you know the mean and all values except one, the missing value is nbar{x} - text{sum of known values}.