1. **Problem Statement:** Find the greatest common factor (GCF) of the given pairs of numbers. 2. **Formula and Rules:** The GCF of two numbers is the largest positive integer that divides both numbers without leaving a remainder. 3. **Step-by-step Solutions:** **1) GCF of 8 and 18:** - Prime factors of 8: $2 \times 2 \times 2$ - Prime factors of 18: $2 \times 3 \times 3$ - Common prime factors: $2$ - GCF = $2$ **2) GCF of 10 and 16:** - Prime factors of 10: $2 \times 5$ - Prime factors of 16: $2 \times 2 \times 2 \times 2$ - Common prime factors: $2$ - GCF = $2$ **3) GCF of 9 and 12:** - Prime factors of 9: $3 \times 3$ - Prime factors of 12: $2 \times 2 \times 3$ - Common prime factors: $3$ - GCF = $3$ **4) GCF of 20 and 24:** - Prime factors of 20: $2 \times 2 \times 5$ - Prime factors of 24: $2 \times 2 \times 2 \times 3$ - Common prime factors: $2 \times 2$ - GCF = $4$ 4. **Summary:** The GCFs are: - 8 and 18: $2$ - 10 and 16: $2$ - 9 and 12: $3$ - 20 and 24: $4$