What is the greatest common factor of 90, 36, 54 and 18?

To find the greatest common factor (GCF) of 90, 36, 54, and 18, follow these steps:

1. First, find the factors of each number:

   • The factors of 90 are: 1, 2, 3, 5, 6, 9, 10, 15, 18, 30, 45, 90
   • The factors of 36 are: 1, 2, 3, 4, 6, 9, 12, 18, 36
   • The factors of 54 are: 1, 2, 3, 6, 9, 18, 27, 54
   • The factors of 18 are: 1, 2, 3, 6, 9, 18

2. Next, identify the common factors of these numbers:

   • The common factors are: 1, 2, 3, 6, 9, 18

3. The greatest of these common factors is 18.

So, the greatest common factor of 90, 36, 54, and 18 is 18.