1. Prime Numbers and Prime Factorization
LESSON 4-3
Additional Examples
List the factors of each number.
a. 24
1  Write factor pairs. Start with 1.
2  12, 3  8, 4  6 2, 3, and 4 are factors. Skip 5,
since 24 is not divisible by 5.
6  Stop when you repeat factors.
The factors of 24 are 1, 2, 3, 4, 6, 8, 12, and 24.

2. Prime Numbers and Prime Factorization
LESSON 4-3
Additional Examples
(continued)
b. 35
1  Write factor pairs. Start with 1.
5  7 Skip 2, 3, and 4, since 35 is not
divisible by 2, 3, or 4. 5 is a factor.
Skip 6, since 35 is not divisible by 6.
7  Stop when you repeat factors.
The factors of 35 are 1, 5, 7, and 35.

3. Prime Numbers and Prime Factorization
LESSON 4-3
Additional Examples
Tell whether each number is prime or composite. Explain.
a. 61
b. 65
Prime; 61 has
only two factors,
1 and 61.
Composite; 65 is divisible by 5,
so it has more than two factors.

4. Prime Numbers and Prime Factorization
LESSON 4-3
Additional Examples
Find the prime factorization of 90.
Method 1 Using a division ladder.
2 90 Divide 90 by the prime number 2. Work down.
3 45 The result is 45. Divide by the prime number 3.
3 15 The result is 15. Divide by 3 again.
5 The prime factorization is 2  3  3  5.
Method 2 Using a factor tree.
90 Since the sum of the digits of
90 is 9, 90 is divisible by 3.
90 = 3  30
3 30
Circle the prime numbers
as you find them.
30 = 3  10
3 10
10 = 2  5
2 5
The prime factorization of 90 is 2  32  5.