There are 3 ways of determining whether a number is prime or composite.
Check if the number is even. If it is, it's 100% composite
If the number is odd, then look at its last digit. If it's 2, 4, 6, 8, 0 or 5, then it is composite.
If the last digit is not 2, 4, 6, 8, 0 or 5, look at the factors of the given number. If it has 2 factors, then it's prime. If it has more than 2 factors, it's composite.
