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"Let us strive to make each moment beautiful."
Saint Francis DeSales
painting by Katie Bergenholtz

Eratosthenes Sieve

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Since we have been working with fractions, and therefore prime numbers, I decided to teach James about Eratosthenes Sieve. Eratosthenes was a Greek mathematician who, among other things, created a simple way of finding prime numbersprime number is a whole number greater than 1 that has no positive divisors other than 1 and itself.You can just use a 100's chart for this exercise. First cross out the numeral 1 because it cannot help be used to build any other numbers. Circle the numeral 2 as it is the first prime number and cross out any numeral that can be made with a 2. Circle 3 as the next prime and cross out any numeral that can be made with a 3.Continue with the numerals, crossing out numerals in this manner.Through this process, you will sieve out all numbers, leaving just prime numbers remaining. We will be working with factoring numbers into their primes as a way of finding equivalent forms in fractions next week.


  1. How have I not heard of this? So cool!

  2. This is SUCH a cool-i-o idea! I have been working with Jungle Girl on fractions a bit, so this activity would be a wonderful addition to our studies!

    Once again, you amaze me, Mama...

  3. You know, I vaguely remember doing this before in junior high and thinking it was the coolest thing ever. I've got a bit of a math nerd in me at times.


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