Greatest Common Factor
Presentation
•
Mathematics
•
5th Grade
•
Easy
+3
Standards-aligned
Sheila Dale
Used 392+ times
FREE Resource
8 Slides • 5 Questions
1
Greatest Common Factor (GCF)
2
Vocabulary
1. Factors- #'s multiplied together to get a product. (5x2=10, 5 and 2 are factors of 10)
2. Greatest common factor- the largest factor that two or more numbers have in common.
3. prime numbers- #'s with exactly 2 factors. (2,3,5,7,11,13,17,...)
4. composite numbers- #'s with more than 2 factors. (4,6,8,9,10,12,14,...)
3
Poll
Is the number 0 prime, composite, or neither?
prime
composite
neither
4
Poll
Is the number 1 prime or composite?
prime
composite
neither
5
Special cases 0 and 1:
If all numbers are either prime or composite, what about 0 and 1?
0 is considered neither prime or composite because 0 has an infinite number of factors. Every number is a factor of 0.
1 is considered neither prime or composite because 1 has only one factor (1). When you have a double factor then you only use it as a factor one time.
6
Is each number prime, composite, or neither?
45
19
100
22
0
51
7
Divisibility Rules: Shortcuts to help determine if numbers are factors of a number.
2 - is the last digit an even number
3 - is the sum of the digits divisible by 3
4 - are the last 2 digits divisible by 4
5 - is the last digit a 0 or 5
6 - is the number divisible by both 2 and 3
9 - is the sum of the digits divisible by 9
10 - is the last digit a 0
8
Steps to find the GCF:
Find ALL factors of each number.
Write the factors in numerical order from least to greatest.
Find the common factors (CF)
The greatest of the common factors is the GCF.
Show all work in a neat and orderly way.
9
Find the GCF of 12 and 20
Factors of 12 Factors of 20
1 x 12 1 x 20
2 x 6 2 x 10
3 x 4 4 x 5
12 = 1, 2, 3, 4, 6, 12
20 = 1, 2, 4, 5, 10, 20
Common factors (CF) of 12 and 20
CF = 1, 2, 4
GCF = 4
10
Practice:
What is the GCF of 24 and 40?
24 =
40 =
CF =
GCF =
What is the GCF of 9 and 22?
9 =
22 =
CF =
GCF =
11
Multiple Select
EXIT TICKET
If all numbers are either prime or composite, what about 0?
prime, because 0 has exactly 2 factors
composite, because 0 has more than two factors
neither, because 0 has infinite number of factors.
12
Fill in the Blanks
Type answer...
13
Poll
Do you understand today's lesson?
Yes, I totally got this!
I have no idea how to do this.
I need to practice a little to understand better.
Greatest Common Factor (GCF)
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