What is the greatest common factor of 16 and 40?

The greatest common factor (GCF) of 16 and 40 is 8. This is because 16 can be broken down into the factors of 2 * 2 * 2 * 2, while 40 can be broken down into the factors of 2 * 2 * 2 * 5. The largest factor that is common to both 16 and 40 is 2 * 2 * 2, which equals 8.