Probability & Statistics

Averages and range

Mean $= \dfrac{\text{sum of values}}{\text{number of values}}$.
Median — the middle value when ordered (mean of the two middle values for an even count).
Mode — the most frequent value.
Range $= \text{largest} - \text{smallest}$ (a measure of spread).

For a frequency table, the mean is $\dfrac{\sum fx}{\sum f}$. For grouped data, use the midpoint of each class as an estimate of $x$.