Question

What is the greatest common factor of 28 and 42?

Answer 1

Let's find the prime factors of 28 and 42 using ladder method


Prime factors of 28: 28 = 2 × 2 × 7
Prime factors of 42: 42 = 2 × 3 × 7

The product of common prime factors of two numbers gives the GCF of those two numbers
$\therefore$ The greatest common factor of 28 and 42 is 2 $\times$ 7 = 14.