Download Finding the GCF/LCM using Prime Factorization

Finding the GCF/LCM using Prime Factorization
Steps for Finding LCM/GCF
Use a factor tree to find the prime factorization of both numbers. (Reorder prime factorization from least to
1.
greatest).
18
30
2.
Circle prime factors that are the same for both numbers.
For example:
18 2X3X3
30 - 2 X 3 X 5
3.
Draw a Venn Diagram and label each circle.
4.
Place the prime factors that can be found in both numbers in the center of the Venn Diagram. (Hint: only write the
number once!)
5.
Write the remaining prime factors for each number in the larger circle
6.
To find GCF multiply only the numbers in the middle of the two circles.
7.
To find LCM multiply ALL numbers in the Venn Diagram.
Let‛s Have Some Fun…………………..
Use prime factorization to find the GCF and LCM of each pair of numbers.
1.
24, 48
GCF_______
LCM ______­­­_
2.
56, 35
GCF________
LCM _______
3.
29, 87
GCF________
LCM _______
4. 30, 42, 15
Hint: Draw 3 circles!!!!!!
GCF________
LCM_______
5. Complete Attachment D “Applying Prime Factorization- Grade 6”
1
Finding the GCF/LCM using a Factor Rainbow
Steps for Finding GCF
1.
Make a Factor Rainbow for each number by listing the factor pairs for each number. Start with the
factors 1 and the number itself.
Example:
3.
18: ___
___
30: ___
___
Continue the Factor Rainbow by listing the remaining factor pairs starting with the least to greatest.
Example:
18: 1, __,__,
__, __, 18
30: 1, __, __,__,
__,__, __, 30
The Factor Rainbow is complete when the numbers meet in the middle or no more factors remain.
4.
Circle the greatest factor that is common in both numbers
2.
Practice:
1.
21, 25
2.
42, 56
3.
45, 75, 30
4.
48, 60
Finding the GCF/LCM using a Factor Rainbow Continued
Steps for Finding LCM
1.
List multiples of each number.
2.
Continue until you find the first multiple that appears for both numbers.
3.
This is the LCM!
Practice:
1.
4,6
2.
8,12
3.
6,15
4.
9,21
5.
5,6
6.
Complete___________________________
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