Prime Factoring

Prime Number, Factors, Multiple, HCF and LCM

presentation by Ms. Hall

Objectives: Students should be able to

• find the prime factors of numbers using repeated division or tree method.

• calculate the HCF using the prime factorization method.

• calculate the LCM using the prime factorization method.

• Solve worded problems with LCM and HCF.

Prime Numbers

Prime numbers are numbers that have only 2 factors: 1 and themselves. 

Prime factor can be found using:

• Repeated Division

• Factor Tree

Repeated Division

Th is method of prime factorization is used to “break down” or express a given number as a product of prime numbers.
For example, the factors of 64 and 80 are as such:

INDEX FORM

 $64\ =\ 2\times2\times2\times2\times2=2^{5\ }$ 

  $80\ =2\times2\times2\times5=\ \ 2^{3\ }\times\ 5$  

Factor Tree

A factor tree shows the prime factors of a composite number in a "tree-like" form. For example, the factors for 72 are as such.

INDEX FORM

 $72\ =\ 2\times2\times2\times3\times3=2^{3\ }\times\ 3^2$