You will need

* A grid containing each of the numbers from one to one hundred. You can download one here

* Several colours of pencil or texta

What to do

In this activity, you will find all the prime numbers under 100. A prime number can’t be divided evenly by any whole number except one and itself. For example, three is a prime number. Six can be divided evenly by two and three, so it isn’t a prime.

1. Start out by circling 2. Two is a prime number because it can only be divided by one and two. However, any other number that is divisible by two isn’t prime. Using one colour of pencil or texta, cross out every other even number. You should find they form neat rows.

2. Now circle 3. Three is also a prime number, but any other multiple of three is not, so cross out all the multiples of three with a different coloured texta. You’ll notice these run in diagonal lines across the page. Continue reading Try this: The sieve of Eratosthenes