Greatest Common Factors through lists
It is possible to find the Greatest Common Factor (GCF) of two or more numbers by simply listing the factors of each number, circling the ones they all have in common, and then identifying the largest circled number.
EXAMPLE: To find the Greatest Common Factor of 12 and 20
(Remember, GCF is the largest number that will divide each number given with NO remainders)
1st:
12 = 1, 2, 3, 4. 6. 12 list the factors of the first number
20 = 1, 2, 4, 5, 10, 20 list the factors of the second number
GCF =
2nd:
12
= 1, 2, 3, 4. 6. 12 circle numbers that show
up in both lists
20 = 1, 2, 4, 5, 10, 20
GCF =
3rd:
12
= 1, 2, 3, 4. 6. 12 the LARGEST (GREATEST)
one circled is GCF
20 = 1, 2, 4, 5, 10, 20
GCF = 4
EXAMPLE
24
= 1, 2, 3, 4, 6., 8, 12, 24
30 = 1, 2, 3, 5, 6, 10, 15, 30
GCF = 6
Problems
For the numbers given below, find the Greatest Common Factor (GCF) of each group.
1) 2)
12
= 20
=
16
= 8 =
GCF GCF
=
3) 4)
25
= 22 =
18
= 33 =
GCF GCF
=
Problems
For the numbers given below, find the Greatest Common Factor (GCF) of each group.
1) 2)
12
= 20
=
16
= 8 =
GCF GCF
=
3) 4)
12
= 20
=
16
= 8 =
GCF GCF
=
5) 6)
25
= 22 =
18
= 33 =
GCF GCF
=
7) 8)
25
= 22 =
18
= 33 =
GCF GCF
=
9) 10)
12
= 20
=
16
= 8 =
GCF GCF
=
Find two numbers that have the GCF indicated
11) 12)
= =
= =
GCF = 5 GCF = 8
GCF GCF
=