1. **State the problem:** Find the Greatest Common Factor (GCF) of 108 and 100. 2. **Formula and rules:** The GCF of two numbers is the largest number that divides both without leaving a remainder. One way to find it is by prime factorization. 3. **Prime factorization:** - 108 = $2^2 \times 3^3$ - 100 = $2^2 \times 5^2$ 4. **Find common prime factors:** Both have $2^2$ in common. 5. **Calculate GCF:** Multiply the common prime factors: $$GCF = 2^2 = 4$$ **Final answer:** The GCF of 108 and 100 is 4.