Mathematics 5 Quarter 1 Lesson4-Greatest Common Factor.ppt

GCF

1. FINDING THE
GREATEST COMMON
FACTOR
Mathematics 5

2. 06 GCF
Greatest Common Factor
GCF
Greatest means _________
Biggest, Largest, Highest
Common means ________
Share, have the same, be alike
A Factor is _________
A number that exactly divides another number without
any remainders.
1, 2, 3, 4, 6, and 12 are factors of 12.

3. The Greatest Common
Factor (GCF) is the
largest (biggest) number
that divides two or more
numbers without any
remainder.

4. There are 2 methods
for finding the GCF
1. Listing the factors
(rainbow)
2. Continuious Division
Method (ladder)

5. Listing the factors
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.

6. Method 1: Making a List
Step 1:
Find all the factors of both numbers
Example:
ALWAYS start with 1 x ____
1 x 12
2 x __use divisibility rules…does 2 work?
3 x __use divisibility rules…does 3 work?
We are DONE cuz 3 & 4 are right next to each other!!

7. Let’s find all the factors of 18

ALWAYS start with 1 x ____
1 x 18
2 x __ use divisibility rules…does 2 work?
3 x __ use divisibility rules…does 3 work?
4 x __ …does 4 work?
5 x __ use divisibility rules…does 5 work?
We are DONE cuz 3,4,5, 6 … 6 is already on the list so we
are working back up.

8. Make a list to find the GCF of 18 &
30..
18: 1, 2, 3, 6, 9, 18
12: 1, 2, 3, 4, 6, 12
What one is the Greatest?
THE GCF OF 12 & 18 IS 6.

9. 1)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.

10. Continuious Division Method (ladder)
1.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

11. Continuious Division Method
(ladder)
•is a method of
factoring which allows
you to factor two
numbers at once
•Step 1: List each
number in the ladder
Example:

12. Step 2: Factor using a prime
number such as 2, 3, 5, 7, 11, 13,
17, and 19
•Example:

13. Step 3: Multiply the numbers on
the outside of the ladder to get
the GCF.
•Example:

14. Use a ladder to find
the GCF of 27 & 36
327 36
3 9 12
3 4
3 X 3 = 9
So the GCF is 9
3