1. Factors and Prime Factorization
4-2
Factors and Prime Factorization
Course 1
Warm Up
Problem of the Day
Lesson Presentation

2. Factors and Prime Factorization
Course 1
4-2
Factors and Prime Factorization
Warm Up
Identify each number as prime or composite.
prime
composite
composite
composite
prime
composite

3. Factors and Prime Factorization
Course 1
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Factors and Prime Factorization
Problem of the Day
At the first train stop, 7 people disembarked. At the second stop, 8 people disembarked. At the fourth stop the last 6 people disembarked. If there were 28 people on the train before the first stop, how many people left at the third stop?
7 people left at the third stop

4. Factors and Prime Factorization
Course 1
4-2
Factors and Prime Factorization
Learn to write prime factorizations of composite numbers.

5. Insert Lesson Title Here
Course 1
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Factors and Prime Factorization
Insert Lesson Title Here
Vocabulary
factor
prime factorization

6. 2 3 = 6 6 ÷ 3 = 2 6 ÷ 2 = 3 4-2 Factors and Prime Factorization
Course 1
4-2
Factors and Prime Factorization
Whole numbers that are multiplied to find a product are called factors of that product. A number is divisible by its factors. 2 3 = 6 6 ÷ 3 = 2
6 is divisible by 3 and 2. 6 ÷ 2 = 3
Factors
Product

7. Factors and Prime Factorization
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Factors and Prime Factorization
Helpful Hint
When the pairs of factors begin to repeat, then you have found all of the factors of the number you are factoring.

8. List all factors of each number.
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Factors and Prime Factorization
Additional Example 1A: Finding Factors
List all factors of each number.
A. 16
Begin listing factors in pairs.
16 = 1 • 16
1 is a factor.
16 = 2 • 8
2 is a factor.
3 is not a factor.
16 = 4 • 4
4 is a factor.
5 is not a factor.
6 is not a factor.
7 is not a factor.
16 = 8 • 2
8 and 2 have already been listed so stop here. 1 2 4 4 8 16
You can draw a diagram to illustrate the factor pairs.
The factors of 16 are 1, 2, 4, 8, and 16.

9. List all factors of each number.
Course 1
4-2
Factors and Prime Factorization
Additional Example 1B: Finding Factors
List all factors of each number.
B. 19
Begin listing all factors in pairs.
19 = 1 • 19
19 is not divisible by any other whole number.
The factors of 19 are 1 and 19.

10. List all factors of each number.
Course 1
4-2
Factors and Prime Factorization
Try This: Example 1A
List all factors of each number.
A. 12
Begin listing factors in pairs.
12 = 1 • 12
1 is a factor.
12 = 2 • 6
2 is a factor.
12 = 3 • 4
3 is a factor.
12 = 4 • 3
4 and 2 have already been listed so stop here. 1 2 3 4 6 12
You can draw a diagram to illustrate the factor pairs.
The factors of 12 are 1, 2, 3, 4, 6, and 12

11. List all factors of each number.
Course 1
4-2
Factors and Prime Factorization
Try This: Example 1B
List all factors of each number.
B. 11
Begin listing all factors in pairs.
11 = 1 • 11
11 is not divisible by any other whole number.
The factors of 11 are 1 and 11.

12. Notice that these factors are all prime.
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Factors and Prime Factorization
You can use factors to write a number in different ways.
Factorization of 12
Notice that these factors are all prime.
1 • 12
2 • 6
3 • 4
3 • 2 • 2
The prime factorization of a number is the number written as the product of its prime factors.

13. Factors and Prime Factorization
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Factors and Prime Factorization
Helpful Hint
You can use exponents to write prime factorizations. Remember that an exponent tells you how many times the base is a factor.

14. Additional Example 2A: Writing Prime Factorizations
Course 1
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Factors and Prime Factorization
Additional Example 2A: Writing Prime Factorizations
Write the prime factorization of each number.
A. 24
Method 1: Use a factor tree.
Choose any two factors of 24 to begin. Keep finding factors until each branch ends at a prime factor. 24 24 • 2 • 12 6 4 2 • 6 3 • 2 2 • 2 2 • 3
24 = 3 • 2 • 2 • 2
24 = 2 • 2 • 2 • 3 3
The prime factorization of 24 is 2 • 2 • 2 • 3, or 2 • 3 .

15. Write the prime factorization of each number.
Course 1
4-2
Factors and Prime Factorization
Additional Example 2B: Writing Prime Factorizations
Write the prime factorization of each number.
B. 42
Method 1: Use a ladder diagram.
Choose a prime factor of 42 to begin. Keep dividing by prime factors until the quotient is 1. 3 42 2 42 2 14 3 21 7 7 7 7 1 1
42 = 3 • 2 • 7
42 = 2 • 3 • 7
The prime factorization of 42 is 2 • 3 • 7.

16. Factors and Prime Factorization
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Factors and Prime Factorization
In Example 2, notice that the prime factors may be written in a different order, but they are still the same factors. Except for changes in the order, there is only one way to write the prime factorization of a number.

17. Write the prime factorization of each number.
Course 1
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Factors and Prime Factorization
Try This: Example 2A
Write the prime factorization of each number.
A. 28
Method 1: Use a factor tree.
Choose any two factors of 28 to begin. Keep finding factors until each branch ends at a prime factor. 28 28 2 • 14 7 • 4 2 • 7 2 • 2
28 = 2 • 2 • 7
28 = 7 • 2 • 2
The prime factorization of 28 is 2 • 2 • 7, or 22 • 7 .

18. Write the prime factorization of each number.
Course 1
4-2
Factors and Prime Factorization
Try This: Example 2B
Write the prime factorization of each number.
B. 36
Method 1: Use a ladder diagram.
Choose a prime factor of 36 to begin. Keep dividing by prime factors until the quotient is 1. 3 36 3 36 2 12 3 12 2 6 2 4 3 3 2 2 1 1
36 = 3 • 2 • 2 • 3
36 = 3 • 3 • 2 • 2
The prime factorization of 36 is 3 • 2 • 2 • 3, or 32 • 23.

19. Factors and Prime Factorization Insert Lesson Title Here
Course 1
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Factors and Prime Factorization
Insert Lesson Title Here
Lesson Quiz
List all the factors of each number.
1. 22
2. 40
3. 51
1, 2, 11, 22
1, 2, 4, 5, 8, 10, 20, 40
1, 3, 17, 51
Write the prime factorization of each number.
4. 32
5. 120 25
23  3  5