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How can you determine if a number is prime by looking at the factors of the number?
A prime number only has two factors. If the number you're looking at has more than two factors, it is not prime.
Determine if 23 is prime or composite?
23 is prime because its only factors are 1 and itself.
Hwo do you determine if a number is prime or composite?
Prime numbers have two factors, composite numbers have more than two.
Why do you need the common prime factors when finding the greatest common factor?
You do not necessarily need the common prime factors when finding the greatest common factor, but with large numbers or numbers for which you cannot easily determine all the factors, using prime factorization to determine the greatest common factor is the easiest method. The greatest common factor can then be determined by multiplying the common prime factors together. For example, when trying to find the greatest common factor of 2144 and 5672, finding all their possible factors to compare could be difficult. So, it is easier to find their prime factors, determine the prime factors they have in common, and then multiply the common prime factors to get the greatest common factor. For descriptions and examples of finding the greatest common factor, see the "Related Questions" links below.
What is the greatest common factor of 119 and 391?
Answer: GCF of 119 and 391 is 17. One way to determine the greatest common factor is to find all the factors of the numbers and compare them. The factors of 119 are 1, 7, 17, and 119. The factors of 391 are 1, 17, 23, and 391 The common factors are 1 and 17. Therefore, the greatest common factor is 17. The greatest common factor can also be calculated by identifying the common prime factors and multiplying them together. The prime factors of 119 are 7 and 17. The prime factors of 391 are 17 and 23. The prime factors in common are a single 17, so the greatest common factor is 17. Once you determine that there are only two prime factors for 119, the easiest way to determine the greatest common factor is to check whether 391 is evenly divided by either 17 or 7, rather than determining the prime factors of 391, too.
