Population growth models using exponential formulas: (1) Simple growth: P = P₀(1 + r)^t; (2) Continuous growth: P = P₀e^(rt). Where P₀ = initial population, r = growth rate, t = time. Doubling time: 2P₀ = P₀(1+r)^T → T = log(2)/log(1+r). Half-life: P₀/2 = P₀(1-r)^T (radioactive decay). Example: P₀=1000, r=5% p.a. After 10 years: P = 1000(1.05)^10 = 1629. Doubling time ≈ 14.2 years. Shortcut: Use logarithms for time calculations. Exam tip: Distinguish growth from decay (positive r vs negative r). Practice: Census, bacteria growth, radioactive decay problems.