Prime or Composite? (Sieve of Erathosethenes)

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Today we worked with the Sieve of Eratosthenes.  This procedure is a way to separate prime numbers from composite numbers.

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We used a 100s chart to keep track of our information.  We began with:

• 1 is NEITHER prime nor composite as it has only 1 factor, so we blacked it out on our chart.
• 2 is the ONLY EVEN prime number, so we colored it and then we marked out all of the multiples of 2.  They are composite because 2 is one of their factors.
• 3 is the next prime number.  We colored it and marked out all of the multiples of 3.
• 5 is the next prime number.  We colored it and marked out all of the multiples of 5.
• 7 is the next prime number.  We colored it and marked out all of the multiples of 7.
• At this point, all of the remaining numbers on the 100s chart are prime.

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