1. FINDING THE GREATEST COMMON FACTOR

2. The greatest common factor (GCF) of 2 or more numbers is the greatest (biggest) number that is a factor of both numbers.

3. There are 2 methods for finding the GCF
1. Listing the factors
2. Using the ladder

4. 1. List the factors of both numbers.
List method
1. List the factors of both numbers.
2. Circle all the factors that they have in common.
3. The GCF is the biggest number that appears on both lists.
Listing the factors

5. Make a list to find the GCF of 18 & 30.
18: 1, 3, 6, 9, 18
30: 1, 2, 3, 5, 6, 10, 15, 30
THE GCF OF 18 & 30 IS 6.

6. LADDER METHOD Draw upside down division box 2. Find a common factor
3. Keep factoring until no common factor exists
4. Multiply numbers on the left side

7. Use a ladder to find the GCF of 27 & 36 3 3
9 12
3 X 3 = 9
So the GCF is 9

8. Finding the Least Common Multiple
LCM: The smallest number that is a multiple of 2 or more numbers.

9. A multiple of a number is the product of the number and a whole number.

10. The first five non-zero multiples of 5 are: 5, 10, 15, 20, 25.
Numbers can have common factors. They also have common multiples.
List the multiples of 12 & 10

11. 3. Keep factoring until no common factor exists
USE THE LADDER METHOD!
Draw upside down
division box
2. Find a common factor
3. Keep factoring until no common factor exists
4. Multiply ALL the numbers on the outside

12. Use a ladder to find the LCM of 27 & 36 3
3 x 3 x 3 x 4 = 108
So the LCM
is 108
9 12 3 3 4