Prime and Composite Numbers

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Prime and Composite Numbers
How can you apply what you know about multiples and factors to determine prime or composite numbers?

Vocabulary Prime - Composite - Multiple - Factor - Factor Pair -
any whole number greater than 1 that has two factors. 1 and itself any whole number greater than 1 that has more than 2 factors the product of any two whole numbers (can be found by skip counting) the numbers multiplied to find a product the two factors in a multiplication sentence

14 array factor pairs factors 1, 2, 7, 14 1 x 14 2 x 7
Now let’s see if there are any equal groups. What about skip counting to find multiples! There are two equal groups of 7 so the factor pair is 2 x 7. You have 1 group of 14 so the factor pair would be 1 x 14. You could make an array and find the factor pairs! Have you ever heard of a factor tree? Do you think you could show me with 14? How do I find factors?

14 > 2 x 7 We used 2 x 7 because the identity property of multiplication says 1 x 14 and 14 is the same thing. Now let’s break it down until we have all primes. We can stop there because 2 and 7 are both prime. Umm…maybe we should ask the class. What about those factor trees? Awesome! Now what? First let’s recall the factor pairs for 14. 1 x 14 and 2 x 7

> > > > _ _ _ 48 12 x 4 6 x 2 2 x 2 3 x 2 2 2 2
1. Count out 48 counters. 12 x 4 > > 2. Break into equal groups. 6 x 2 2 x 2 > _ _ _ 3 x 2 2 2 2 3. Write factor pairs. I wonder what a number tree would look like if I had a bigger number? How can we organize this 4. Try your factor pairs in a factor tree. 5. Multiply your primes to see if you’re correct.

No matter the factor pair you get the same primes.
Make a chart! Number Factor Pairs Factors Prime or Composite 48 1 x 48 2 x 24 3 x 16 4 x 12 6 x 8 1, 2, 3, 4, 6, 8, 12, 16, 24, 48 Composite No matter the factor pair you get the same primes. 48 I wonder if I used another factor pair would my number tree look the same? < 6 x 8 < < 3 x 2 2 x 4 _ _ _ < 3 2 2 2 x 2

You give it a try! Use manipulatives to help you if you need them.
Number Factor Pairs Factors Prime or Composite 36 45 24 18 72 Find the factor pairs. Use the factors in a number tree. Find equal groups. Make arrays. Use manipulatives to help you if you need them.

Go to Stations Teacher Application Computers Flash Cards Table 1