Descriptive Statistics

• Mean: $\bar{x} = \frac{\sum x}{n}$ or $\bar{x} = \frac{\sum fx}{\sum f}$ (grouped).
• Median: middle value. Q2.
• Mode: most frequent.

• Range: max − min.
• IQR: Q3 − Q1.
• Variance: $\sigma^2 = \frac{\sum(x-\bar{x})^2}{n} = \frac{\sum x^2}{n} - \bar{x}^2$.
• Standard deviation: $\sigma = \sqrt{\text{variance}}$.

Box plot: min, Q1, median, Q3, max. Outliers: beyond $Q1 - 1.5 \times IQR$ or $Q3 + 1.5 \times IQR$.