1. Least Common Multiple (LCM) of
2 or 3 numbers

2. Least Common Multiple (LCM)
Finding the
Least Common Multiple (LCM)

3. Finding the
Least Common Multiple (LCM)
Example 1) Find the LCM of 12 and 15
Solution 1)
The multiples of 12 are 12, 24, 36, 48, 60, 72, 84……
The multiples of 15 are 15, 30, 45, 60, 75, 90 ……
Answer: The LCM of 12 and 15 is 60
Solution 2)
The prime factors of 12 = 2 x 2 x 3
The prime factors of 15 = x 5
LCM = = 60
2 x 2 x 3 x 5

4. Finding the
Least Common Multiple (LCM)
Example 2) Find the LCM of 5, 6 and 10
Solution 1)
The multiples of 5 are 5, 10, 15, 20, 25, 30, 35, 40, ….
The multiples of 6 are 6, 12, 18, 24,30, 36, 42, …
The multiples of 10 are 10, 20, 30, 40, 50, …
Answer: The LCM of 5, 6 and 10 30
Solution 2)
The prime factors of 5 =
The prime factors of 6 = 2 x 3
The prime factors of 10 = 2 x
LCM = = 30
2 x 3 x 5

5. Greatest Common factor (GCF) of
2 or 3 numbers

6. Greatest Common Factor (GCF)
Finding the
Greatest Common Factor (GCF)

7. Finding the
Greatest Common Factor (GCF)
Example 1) Find the GCF of 12 and 15
Solution:
The prime factors of 12 = 2 x 2 x 3
The prime factors of 15 = x 5
GCF = = 3 3

8. GCF = 1 Finding the Greatest Common Factor (GCF)
Example 2) Find the GCF of 5, 6 and 10
Solution:
The prime factors of 5 =
The prime factors of 6 = 2 x 3
The prime factors of 10 = 2 x
no common factor
GCF = 1

9. LCM = = 120 GCF = = 4 Finding the LCM and GCF
Example 2) Find the LCM and GCF of 8, 12 and 20
Solution: LCM:
The prime factors of 8 = x 2 x 2
The prime factors of 12 = 2 x 2 x
The prime factors of 20 = 2 x 2 x
LCM = = 120
2 x 2 x 2 x3 x 5
Solution: GCF:
The prime factors of 8 = x 2 x 2
The prime factors of 12 = 2 x 2 x
The prime factors of 20 = 2 x 2 x
GCF = = 4
2 x 2

10. Link to Practice Online
Finding the LCM
Finding the GCF