**Mean** |
$$\bar{x} =
\frac{\sum x_i}{n}$$ |
For values 2, 3, 4, mean = (2+3+4)/3 =
3 |

**Median (Odd)** |
Middle value in ordered set |
For values 1, 3, 5, median = 3 |

**Median (Even)** |
Average of two middle values |
For values 1, 2, 3, 4, median = (2+3)/2 =
2.5 |

**Mode** |
Most frequently occurring value |
For values 1, 2, 2, 3, mode = 2 |

**Standard Deviation
(Population)** |
$$\sigma =
\sqrt{\frac{\sum (x_i - \mu)^2}{N}}$$ |
For values 2, 4, 4, 4, 5, 5, 7, *σ* ≈
1.40 |

**Standard Deviation
(Sample)** |
$$s =
\sqrt{\frac{\sum (x_i - \bar{x})^2}{n-1}}$$ |
For sample values 2, 4, 4, 4, 5, 5, 7,
*s* ≈ 1.51 |

**Range** |
Difference between max and min |
For values 1, 2, 3, 4, 5, range = 5 - 1 =
4 |

**Variance
(Population)** |
$$\sigma^2 =
\frac{\sum (x_i - \mu)^2}{N}$$ |
For values 2, 4, 4, 4, 5, 5, 7, *σ*^{2} ≈ 1.96 |

**Variance (Sample)** |
$$s^2 =
\frac{\sum (x_i - \bar{x})^2}{n-1}$$ |
For sample values 2, 4, 4, 4, 5, 5, 7,
*s*^{2} ≈ 2.29 |