GoldStudent.com - Prime Factoring 2nd tutorial

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This is the second tutorial on how to do prime factoring.

Let's review.

The definition is:

A number's prime factors are the prime numbers that multiplied together give the number.

The tools you'll need to do prime factoring are to learn a few tricks and to know the first few prime numbers.

Let's review.

The first few prime numbers, those less than 20, are 2, 3, 5, 7, 11, 13, 17 and 19.

In the first tutorial we learn some tricks to how to find out if a number is divisible by 2 and by 3 or by 5.

Here we will learn some additional tricks: 1. The first one is that a number is divisible by 6 if it is divisible by both 2 and by 3. In other words, if it's last digit is even and if the sum of it's digits is divisible by 3.
2. Another trick is that a number is divisible by 9 if the sum of its digits is divisible by 9. So, for instance, the number 207 has the sum of its digits 2 + 0 + 7 = 9 which is divisible by 9. Therefore 207 is divisible by 9.
3. Finally, a number is divisible by 10 if it ends in a 0.

Let's do an example:

Let's find the prime factor of the number 2430. 1. First of all 2430 ends in a 0, therefore it is divisible by 10: 2430 = 10 x 243 and because 10 can be written in terms of its prime factors as 2 x 5 we can write: 2430 = 2 x 5 x 243.
2. 243 is not prime. The sum of its digits is 2 + 4 + 3 = 9 therefore is divisible both by 3 and by 9. You can easily show that 243 = 3 x 81.
3. 81 is a perfect square: 81 = 9 x 9 in other words in therms of the prime factors 3 x 3 x 3 x 3.

Therefore we have the final answer:
2430 = 2 x 5 x 3 x 3 x 3 x 3 x 3.

Category:

Education

Tags:

• GoldStudent
• math video
• math tutorial
• prime factoring
• calculate prime factors
• find the prime factors
• divisible