Prime time
A prime number is a numerical number that can be divided, without a remainder, only by itself and by 1. For example, 17 can be divided only by 17 and by 1, whereas 12 can be divided by 1, 2, 3, 4, 6 and 12 which mean 12 is not a prime number.
Some facts:
– The only even prime number is 2. All other even numbers can be divided by 2.
– If the sum of a number’s digits is a multiple of 3, that number can be divided by 3.
– No prime number greater than 5 ends in a 5. Any number greater than 5 that ends in a 5 can be divided by 5.
– 0 and 1 are not considered prime numbers.
– A number greater than 1 and is NOT a prime number is known as a composite number.
Is a number prime?
To prove whether a number is a prime number, first, try dividing it by 2, and see if you get a whole number. If you do, it can’t be a prime number. If you don’t get a whole number, next try dividing it by prime numbers: 3, 5, 7, 11 (9 is divisible by 3) and so on, always dividing by a prime number.
Try out the following activity, drag the numbers below the chalkboard to the correct side. Which ones are prime and which aren’t?