Download I can find the GCF of two whole numbers less than or equal to 100.

Finding the
GCF
I can find the GCF of two whole
numbers less than or equal to
100.
What is a GCF?
The Greatest Common
Factor (G.C.F.) of two
numbers is the largest
number that is a divisor
of both. It can be used to
simplify (or reduce)
fractions.
What is a GCF?
GREATEST
is biggest or
largest.
COMMON is something
shared or in common.
FACTORS are the parts
of multiplication facts.
What is a GCF?
There are multiple ways to
find the GCF
Today we will talk about two of
the following two methods:
1) The Tree Method
(Prime Factorization)
2) Listing Method
Tree Method
1)  Break the number down until
it is only prime numbers
2)  List the number as a
factor of primes
3)  Find all the prime numbers
the two original number
share
4)  Multiply. The product is
the greatest common
factor
Tree Method
Break each number down to prime
factors.
56
84
2 28
42
2
2 14
2
6
7
7
3
2
Prime Factorization
of 56 and 84
56: 2x2x2x7
Circle what
they have in
common
84: 2x2x7x3
Multiply only one row. 2x2x7
The GCF is 28
Tree Method
Break each number down to prime
factors.
63
81
7
9
3
9
3
3 3
9
3 3
Prime Factorization
of 63 and 81
Circle what
they have in
common
63:3X3x7
81:3x3x3x3
Multiply only one row. 3x3
The GCF is 9
Tree Method
3
48
6
56
8
2 4
2
7
4
2
2
2x2x2=6
GCF = 6
8
2
2
2
48 : 2 x 2 x 2 x 2 x 3 56: 2 x 2 x 2 x 7 Tree Method
3
24
6
36
3
4
2
2
9
2 3
24 : 2 x 3 x 3 2 x 3= 6 36 : 2 x 2 x 3 x 3 GCF = 6
3
Now try example 5
through 8 using the
tree method by
yourself!
Exit Slip
Finding the
GCF Activity
I can find the GCF of two whole
numbers less than or equal to
100.
Find the GCF of the
following numbers
26 and 42
Find the GCF of the
following numbers
30 and 40
Find the GCF of the
following numbers
32 and 44
Find the GCF of the
following numbers
27 and 45
Find the GCF of the
following numbers
36 and 48
Find the GCF of the
following numbers
65 and 91
Find the GCF of the
following numbers
84 and 92
Find the GCF of the
following numbers
51 and 75
Find the GCF of the
following numbers
64 and 72
Find the GCF of the
following numbers
99 and 66
Find the GCF of the
following numbers
20 and 24
Find the GCF of the
following numbers
21 and 56
Find the GCF of the
following numbers
18 and 90
Find the GCF of the
following numbers
8 and 64
Find the GCF of the
following numbers
20 and 45
Find the GCF of the
following numbers
18 and 63
Find the GCF of the
following numbers
42 and 48
Find the GCF of the
following numbers
16 and 28
Find the GCF of the
following numbers
30 and 42
Find the GCF of the
following numbers
36 and 72
Find the GCF of the
following numbers
15 and 40
Find the GCF of the
following numbers
24 and 28
Find the GCF of the
following numbers
24 and 32
Find the GCF of the
following numbers
9 and 54
Find the GCF of the
following numbers
40 and 50
Find the GCF of the
following numbers
6 and 36