What is the greatest common factor of 30 45 and 90?

The GCF of 30, 45, and 90 is 15.

One way to approach this is to look at the difference between 30, 45, and 90. The difference between 30 and 45 is 15. The difference between 45 and 90 is 45. The greatest common factor cannot be larger than the smallest difference between the numbers and must be a factor of the difference. The smallest difference is 15. Since 30, 45, and 90 are divisible by 15, the greatest common factor is 15.