# Factor Strings and Prime Factorization

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Factor Strings and Prime Factorization
Everyday Math Lesson 1.9

Lesson Objectives I can tell the difference between powers of ten written as ten raised to an exponent . I can show powers of 10 using whole number exponents I will also go over the essential question(s) for this lesson before presenting the I Can Statements.

Mental Math 2 x 2 = 5 x 6 = 6 * 9 = 2 x 3 = 7 * 3 = 8 * 9 = 3 x 4 =
7 * 6 = 9 * 7 = 4 x 5 = 8 x 5 = 8 * 6 =

Let’s Check Your Homework!

Math Message 8 + 8 and 4 * 4 are two names for the number 16. In your Math Work Journal write at least 5 more names for the number 16. After giving students time to think of their answers, have students share their answers while recording them on the class data pad. Encourage students to think of new ways that aren’t listed. Watch for students who only use addition and subtraction problems; encourage students to think of other operations besides addition and subtraction.

Vocabulary Add this vocabulary word to your Vocabulary Chart:
prime factorization

Introducing Factor Strings
A factor string is a multiplication expression that has at least two factors that are greater than one. Example: a factor string for the number 24 would be 2 x 3 x 4 Explain that the Commutative property applies to factor trees, using the property may help make a longer fractor string.

Your Turn Write another factor string for the number 24; don’t use the same numbers as the example we did together. Ask students to do this in their student work journals.

Let’s Try Again! Make a factor string for the number 7.
What type of number is 7? You may not use 1 in factor strings, and 7 has no other factors except 7 and itself; therefore it is a prime number.

Try this! Find factor strings for the following numbers: 30, 50, 54, and 72.

Factor Rainbows The longest possible factor string for a number is also known as the prime factorization. In order to find prime factorization we can also use a factor tree. I will show students the process of using a factor tree to find prime factorization and let them practice before doing the journal pages.

On Your Own! Try finding the prime factorization of the following numbers using factor trees: 36, 18, and 9. Check answers to assure the students are doing the process correctly.

Finding Factor Strings and Prime Factorization
With your assigned partner, complete Student Journal Pages 25 and 26. You will have 20 minutes to complete this assignment, when you hear the bell, return to your seat and be ready to share your answers.

Let’s Play “Name That Number”!
Turn to page 325 in your SRB and read about how to play “Name That Number”. With your assigned partner, you will have 15 minutes to play. 

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