Finding the
Greatest
Common
Factor
The greatest
common factor
of two or more
numbers is the
greatest number
that is a factor of
every number.
There are two
methods for finding
the GCF.
1. Listing the factors
2. Using the Ladder
To find the GCF of two
numbers using a list, list the
factors of one number. Then
list the factors of the second
number. The GCF is the
greatest value that appears on
both lists.
1. Make a list to find the
GCF of 18 and 30
18: 1, 2, 3, 6, 9, 18
30: 1, 2, 3, 5, 6, 10, 15, 30
THE GCF of 18 and 30 is 6.
To find the GCF of two
numbers using the ladder
method, determine a prime
number that you can divide
evenly into each number.
Write the number on the side
and divide. Continue as far as
you can!
2. Use a ladder to find
the GCF of 27 and 36
3 27 36
3 9 12
3 4
3 x 3 =9
so the
GCF is 9
Finding the
Least
Common
Multiple
The Least Common
Multiple of two or more
numbers is the smallest
number that is a multiple
of every number.
There are two methods
for finding the LCM.
1.Listing the
multiples
2.Using the Ladder
To find the LCM of two numbers
using a list, list the first ten
multiples of one number. Then list
the first ten multiples of the
second number. The LCM is the
smallest value that appears on
both lists. (You might need to add
more than the first ten multiples of
each number)
1.Make a list to find the LCM
of 6 and 15.
6: 6, 12, 18, 24, 30, 36, 42,
48, 54, 60
15: 15, 30, 45, 60, 75, 90,
105, 120, 135, 150
To find the LCM of two
number using the ladder
method,
determine
a
number that you can
divide evenly into each
number.
Write
the
number on the side and
divide. Continue as far as
you can!
2. Use the ladder method to
find the LCM of 27 and 36.
3
3
27
9
3
36
12
4
3x3x3x4 =
9 x 12=
108
2. Use the ladder method to
find the LCM of 20 and 24.
20
24
2. Use the ladder method to
find the LCM of 9 and 12.
9
12
2. Use the ladder method to
find the LCM of 8 and 6.
8
6