1, 2, 3 and 6
Okay. Give us a pair of numbers.
It is common to group factors in pairs with parentheses surrounding each pair.
The common prime factors of 18 and 30 are 2 and 3.
Since 1, known as the "multiplicative identity", cannot be counted as a factor, there are many pairs of numbers that do not have common factors, such as 2 and 3, 2 and 5, and 3 and 5. There are many pairs of composite (not prime) numbers without common factors, such as 4 and 9. Also, since prime numbers do not have factors, any pair of primes cannot have a common factor, though a pair in which one number is prime may, e.g. 5 and 10.
The factors of 14 are: 1, 2, 7, 14 The factors of 49 are: 1, 7, 49 The common factors are: 1, 7 The Greatest Common Factor: GCF = 7
The common factor is 1.
Okay. Give us a pair of numbers.
Just 1.
1, 2 and 4
All numbers have common multiples.
Even numbers.
I suggest factoring each pair of numbers, and checking whether they have, or don't have, common factors. A pair of numbers is said to be "relatively prime" if they have no common factors (their greatest common factor is 1). For larger numbers, Euclid's algorithm could be used, but for such small numbers, factoring is probably faster.
Yes, a pair of numbers can have fewer than two common factors. This only happens when the numbers are co-prime -- that is, when the numbers have only one common factor. In that case, the common factor is always 1.
20 and 40 have 4 and 5 as common factors.
21 and 42
12 and 24
12 and 24