concepts:
  - id: descriptive-statistics
    title: Descriptive Statistics
    description: Measures of center and spread.
    prerequisites: []
    mastery_signals:
      - Explain mean, median, and variance.
  - id: probability-basics
    title: Probability Basics
    description: Basic event probability and conditional probability.
    prerequisites:
      - descriptive-statistics
    mastery_signals:
      - Compute a simple conditional probability.