Identifying Even Composite Numbers
Grade 4 Eureka Math students learn that all even numbers greater than 2 are composite numbers. An even number is any multiple of 2, meaning 2 is always a factor. Since a composite number has more than two factors, any even number greater than 2 qualifies: for example, 10 has factors 1, 2, 5, and 10, while 38 = 2 × 19 has factors 1, 2, 19, and 38. The only even prime is 2 itself, because its only factors are 1 and 2. This rule helps students quickly classify large even numbers without fully factoring them.
Key Concepts
All even numbers greater than 2 are composite numbers. This is because they are divisible by 2, meaning they have 2 as a factor in addition to 1 and the number itself.
Common Questions
Why are all even numbers greater than 2 composite?
They are divisible by 2, giving them at least three factors: 1, 2, and themselves. A composite number is defined as having more than two factors.
Is 2 prime or composite?
2 is prime. Its only factors are 1 and 2, which is exactly two factors, so it is not composite.
Is 38 a prime or composite number?
Composite. 38 = 2 × 19, so its factors are 1, 2, 19, and 38.
How can you identify an even composite number quickly?
If a number greater than 2 is even (ends in 0, 2, 4, 6, or 8), it is automatically composite because 2 divides it.
What is the difference between prime and composite numbers?
A prime number has exactly two factors: 1 and itself. A composite number has more than two factors.