PRIME & COMPOSITE NUMBERS

In class, we learned how to determine if a number is prime or composite. Prime Numbers have only 2 factors whereas composite numbers have many.  All even numbers are composite except the number 2.  The number 2 is the only even number that is prime because it only has two factors 1 and itself (2).  The number 1 is neither prime or composite where it’s only factor is 1.

To determine if an odd number is prime or composite we learned to apply the divisibility rule for 3.  If the sum of the digits is divisible by 3 then the number is composite.  If the sum is not divisible by 3 the number is prime.

Example:  27 (composite)                          18001 (prime)

2 + 7 = 9 – is divisible by 3         1 + 8 + 0 + 0 + 1 = 10 – is not divisible by 3

LOWEST COMMON MULTIPLE (LCM) & GREATEST COMMON FACTOR (GCF)

In class we’ve also been learning how to identify the Lowest Common Multiple (LCM) and Greatest Common Factor (GCF) of two numbers.

Example:

4 and 36

4: 4, 8, 12, 16, 20, 24, 28, 32, 36

36: 36, 72, 98

LCM = 36

Factors of 4: 1, 2, 4

Factors of 36: 1, 2, 4, 6, 9, 18, 36

GCF= 4