Divisibility rules help you find the factors of a number. Once you've found the factors for two or more numbers, you can find what they have in common. Take 231 and 321. If you know the divisibility rules, you know that they are both divisible by 3, so 3 is a common factor.
Suppose you were trying to find the prime factorization of 123. You know that half of the divisors will be less than the square root. Since the square root is between 11 and 12, you only need to test 2, 3, 5, 7 and 11 as prime factors. If you know the rules of divisibility, you already know that 2 and 5 aren't factors and 3 is. It saves time.
By the rules of divisibility, you know that 40 is divisible by 1, 2, 4 and 5. Dividing those numbers into 40 gives you the rest. (40,1)(20,2)(10,4)(8,5)
There is always a common factor. If there are no common prime factors, the GCF is 1.
There cannot be a 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.
First, find the prime factorization. Use a factor tree. 189 63,3 21,3,3 7,3,3,3 All the other factors will be combinations of these. There are eight altogether. You know that 1, 3 and 7 are factors. The rules of divisibility tells you that 9 is as well. Dividing them into 189 gives you the rest. 1, 3, 7, 9, 21, 27, 63, 189
A number is a multiple of 312 if it's a multiple of 3, 8 and 13 at the same time
they can help you by finding the two factors of the number given
Factors are divisors. If you know the divisibility rules, you know that 80 is divisible by 1, 2, 4, 5 and 8. If you divide 80 by those numbers, you find the other half of the factor pairs.
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You use divisibility rules t determine whether a particular number is (or is not) a factor of another number. If it is a factor, you can reduce the numbers involved to smaller numbers.You might want to find factors to simplify fractions or to add or subtract factions.
The divisibility rules will show that 53 is not divisible by anything other than 1 and itself. Since it is already prime, it doesn't have a factorization.
26
If you know that a number is divisible by three, then you know that three and the number that results from the dividing are both factors of the original number. If you know that a number is not divisible by three, then you won't waste time performing that function. It's rare that the first factor other than one isn't a number between two and ten. If you know the divisibility rules, it will make factoring easier and faster.
Suppose you were trying to find the prime factorization of 123. You know that half of the divisors will be less than the square root. Since the square root is between 11 and 12, you only need to test 2, 3, 5, 7 and 11 as prime factors. If you know the rules of divisibility, you already know that 2 and 5 aren't factors and 3 is. It saves time.
Those for 1, 2, 4, 5 and 8.
By the rules of divisibility, you know that 40 is divisible by 1, 2, 4 and 5. Dividing those numbers into 40 gives you the rest. (40,1)(20,2)(10,4)(8,5)
You can test successive prime numbers to see if your number is divisible by them, but knowing the divisibility rules will help you eliminate some steps, depending on what your number is. If your number is odd, you don't have to test for 2. If the sum of your number's digits do not total a multiple of 3, you don't have to test for 3. If your number doesn't end in a 5 or 0, you don't have to test for 5. Just by looking at your number, you can include or eliminate the three most common primes if you know the rules of divisibility.