Welcome to my math blog! The purpose of this blog is to help you stay informed about our learning and experiences that have taken place during our math class. I have also included links your child (and you) may want to use in order to supplement math learning in 5th grade.

## Wednesday, January 6, 2016

### Prime or Composite? (Sieve of Erathosethenes)

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

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.