Prime Factors

You will learn to:

    -    Express a number as a product of its prime factors
    -    Find the prime factors of a number

Method

Sometimes you may be asked to express a number as a product of its' prime factors, or you may be asked to find the numbers prime factors. This is useful for finding the HCF and LCM of numbers, as we will see next lesson.

Suppose we are asked: 
        Express 550 as a product of it's prime factors
        
1. Divide the number by a prime number, e.g. 5.
        550 / 5 = 110

2.  5 Is a prime factor. The number can still be divided, so let's halve it.
        110 / 2 =  55

3. 2 is a prime factor. 55 can be divided by 5.
         55 / 5 = 11

4. 5 and 11 are both prime factors. This means that the prime factors of 550 are: 5, 11, 5, 2; Or, more naturally, 2, 5, 5, 11.

5. We were asked to express 550 as a product of its primes, so, instead of listing them, we write:

            550 = 2 X 5 X 5 X 11

6. Don't believe me?

            550 = (2 X 5) X (5 X 11)
            550 = 10 X 55
            - Prepare to be blown away...
            550 = 550!

Remember that all numbers can be expressed as a product of its primes