1. The Ladder Method For Finding GCF and LCM
Becky Afghani, LBUSD Math Curriculum Office, 2003

2. Becky Afghani, LBUSD Math Curriculum Office, 2003
The Ladder Method...
is a method of factoring which allows you to factor two numbers at once in order to…
find the GCF of the two numbers
find the LCM of the two numbers
Becky Afghani, LBUSD Math Curriculum Office, 2003

3. Use the ladder to factor 6 and 8.
You will divide out any common factors of the two numbers 2 6 8 3 4
What number goes
into both 6 and 8?
Now divide both
6 and 8 by the 2
Does any # besides 1
go into both 3 and 4?
No? Then you are done
making the ladder.
Becky Afghani, LBUSD Math Curriculum Office, 2003

4. What is the Greatest Common Factor (GCF) of 6 and 8?
The GCF is the product of all the numbers on the left. 2 6 8
The GCF of
6 and 8
is 2. 3 4
Becky Afghani, LBUSD Math Curriculum Office, 2003

5. Let’s find the Least Common Multiple (LCM) of 6 and 8
The LCM is the product of all the numbers on the left and the bottom. x 2 6 8
The LCM of
6 and 8
is 24. 3 4
=24
Becky Afghani, LBUSD Math Curriculum Office, 2003

6. Let’s try some bigger numbers.
Divide out all the common factors down the left side. 2 24 60
What number
goes into both
24 and 60?
Does any #
besides 1
go into both
12 and 30? 2 12 30
How about
6 and 15?
Anything else? 3 6 15
No?
You’re done. 2 5
Becky Afghani, LBUSD Math Curriculum Office, 2003

7. Becky Afghani, LBUSD Math Curriculum Office, 2003
Find the GCF. x
The GCF of
24 and 60
is 12. 24 60 2 12 30 6 15 3 5 = 12
Becky Afghani, LBUSD Math Curriculum Office, 2003

8. Becky Afghani, LBUSD Math Curriculum Office, 2003
Find the LCM. x
The LCM of
24 and 60
is 120. 24 60 2 12 30 6 15 3 5 =
120
Becky Afghani, LBUSD Math Curriculum Office, 2003

9. Practice. Find the LCM and GCF for 28 and 42.7 14 21 2 3
Becky Afghani, LBUSD Math Curriculum Office, 2003