Question

What is the greatest common factor of 72 and 90?

• A. 9
• B. 18
• C. 6
• D. 15

Answer 1

The correct option is B 18

Step 1: Let's find the prime factors of 72 and 90 using ladder method


Step 2: List the prime factors from the ladder method
Prime factors of 72: 72 = 2 × 2 × 2 × 3 × 3
Prime factors of 90: 90 = 2 × 3 × 3 × 5

Step 3: Let's find the GCF of 72 and 90 by multiplying the common factors 2, 3, and 3.
2 × 3 × 3 = 18
$\therefore$ The greatest common factor of 72 and 90 is 2 × 3 × 3 = 18.