What is the greatest common factor of 43 and 81?

Answer 1

You need 2 or more numbers to do common factors, because it needs to be a factor which is COMMON to the numbers)

The Greatest Common Factor (GCF), or Highest Common Factor (HCF), of two or more non-zero integers, is the largest positive integer that divides the numbers without a remainder.
There cannot be a greatest common factor of just one number. To be common there need to be at least two numbers. If you find all the factors of two or more numbers, and you find some factors are the same ("common"), then the largest of those common factors is the Greatest Common Factor.

Answer 2

To determine the GCF, first identify the prime factors for each number.

45 = 3 x 3 x 5

81 = 3 x 3 x 3 x 3

The common factors of both numbers are 3 and 3.

The Greatest (or Highest) Common Factor is therefore 3 x 3 = 9.

Answer 3

43 is a Prime number and its only factors are therefore 1 and 43.

As 81 is not divisible by 43 then the only factor common to both numbers is 1.

Answer 4

The GCF is 9.

Answer 5

It is: 1