What are the greatest common factors of 45 and 81?

Answer 1

Short answer: There are none.

There is neither a greatest common factor nor common factors of a single number, such as 81, 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 81 are 1, 3, 9, 27, and 81.

Examples:

The common factors of 18 and 81 are 1, 3, and 9; the greatest common factor is 9.

The common factors of 20 and 81 are only 1; the greatest common factor is 1.

The common factors of 39 and 81 are 1 and 3; the greatest common factor is 3.

The common factors of 81 and 243 are 1, 3, 9, 27, and 81; the greatest common factor is 81.

Answer 2

The prime factors of 45 are 3, 3 and 5

The prime factors of 81 are 3, 3, 3 and 3.

So two 3s are common to both numbers so 3 x 3 = 9 and that is the greatest common factor of the two.

Answer 3

GCD: 9

LCM: 567

Answer 4

9