Normal distribution: Bell curve, symmetric, mean=median=mode. PDF: f(x) = (1/(σ√(2π))) × e^(-(x-μ)²/(2σ²)). Properties: (1) ~68% within μ±σ; ~95% within μ±2σ; ~99.7% within μ±3σ; (2) Total area = 1; (3) Defined by μ, σ. Standard normal Z: Z = (X - μ)/σ. Example: IQ~N(100,15). P(X<115) = P(Z<1) ≈ 0.8413. Solving: Standardize using Z-score. Use standard normal table. Applications: Heights, test scores, measurement errors. Exam tip: Memorize empirical rule. Use Z-table for probabilities. Practice: Various normal probability problems.