Prime and Composite Numbers, Activity Using Arrays to Find Factors
Prime and composite numbers are explored in Grade 4, Saxon Math Intermediate 4 Chapter 6, using arrays to find factors. A prime number has exactly two factors—1 and itself—making it the basic building block of all whole numbers. A composite number has more than two factors. For example, 27 is composite because it is divisible by 1, 3, 9, and 27. Students use arrays to visually discover factors and distinguish between prime and composite numbers, building skills essential for fraction work and number theory.
Key Concepts
New Concept A prime number is a counting number that has exactly two different factors, itself and 1. A counting number with more than two factors is a composite number.
What’s next Next, you’ll use this definition to practice identifying prime numbers, find factors, and solve problems involving multiples.
Common Questions
What is a prime number?
A prime number has exactly two factors: 1 and itself. Examples include 2, 3, 5, 7, 11, and 13.
What is a composite number?
A composite number has more than two factors. For example, 27 has factors 1, 3, 9, and 27, so it is composite.
Is 1 a prime or composite number?
Neither. The number 1 has only one factor (itself), so it does not meet the definition of prime (exactly two factors) or composite (more than two).
Are all odd numbers prime?
No. Many odd numbers like 9, 15, 21, and 27 are composite because they have factors other than 1 and themselves. For example, 9 equals 3 times 3.
How do arrays help find factors?
An array arranges objects in equal rows and columns. Each valid array for a number reveals a factor pair, helping students see all the ways a number can be divided evenly.
What is the smallest prime number?
The smallest prime number is 2. It is also the only even prime number, since all other even numbers are divisible by 2.