What is the greatest common factor of 40?

Answer 1

There is neither a greatest common factor nor common factors of a single number, such as 40, because there cannot be any form of common factor without two or more numbers to compare. Common factors are factors that the numbers being compared have in common. The greatest common factor is the largest factor that all the numbers being compared have in common. Thus, since there are not two or more numbers to compare, there are neither common factors nor a greatest common factor.

The factors of 40 are 1, 2, 4, 5, 8, 10, 20, and 40.

The prime factors of 40 are 2, 2, 2, and 5.

Examples:

The common factors of 16 and 40 are 1, 2, 4, and 8; the greatest common factor is 8.

The common factors of 40 and 55 are 1 and 5; the greatest common factor is 5.

The common factors of 36, 40, and 96 are 1, 2, and 4; the greatest common factor is 4.

Answer 2

A single number cannot have a highest common factor because "common" refers to factors that two or more numbers have in common. You have only one number.