5-1

1
5-1 5-2Prime Factors and Greatest Common Factors

• Vocab
• Prime Numbers(5-1) A whole number with exactly 2
  factors (1 and itself) ex 17 1,17
• 1 is not Prime!!
• Composite Numbers(5-1) A whole number with more
  than 2 factors ex 8 1,2,4,8
• Prime Factorization Write a composite number as
  a product of only primes. 18 2x3x3
• Greatest Common factor The largest factor 2 or
  more numbers share (will divide into both numbers
  evenly)

2

• To find the GCF using lists of factors
• Write all the factors of the following numbers
• 20
• 24
• 201, 2, 4, 5, 10, 20
• 241, 2, 3, 4, 6, 8, 12, 24

Factors of 20
Factors of 24
3 6 8 24 12
1 2 4
5 10 20
The greatest common factor(GCF) is 4
3

• Find the GCF of 6 and 12
• 61,2,3,6
• 121,2,3,4,6,12

12
1 2 3 4 6
The GCF is 6
4
Find GCF with Prime Factors

• Find the Prime factors of 45 and 36
• 36 6 x 6
• 2x3x2x3 ?all primes
• 2x2x3x3?rewrite in order
• 45 9 X 5
• 3x3x5?all primes (in order)
• So 36 2x2x3x3
• 45 3x3x5
• 3x 3 is on both lists so the GCF is 3x3 9

5

• Find the GCF of 30 a2 and 18 a3b
• 30 a2
• 2x3x5xaxa
• 18a3b
• 2x3x3xaxaxaxb
• 2x3xaxa is on both lists so
• the GCF is 2x3xaxa6a2

6

• Period 6 7
• 5-1/199/33-35,50,51
• 5-2/205-206/26-33,39-44,47
• Periods 1, 3, 8
• 5-2/205-206/9-19 o,39-44,46,47

Assignment