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Prime Numbers Eratosthenes Sieve By Monica Yuskaitis

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Copyright © 2000 by Monica Yuskaitis Eratosthenes (ehr-uh-TAHS-thuh-neez) Eratosthenes was the librarian at Alexandria, Egypt in 200 B.C. Note every book was a scroll.

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Copyright © 2000 by Monica Yuskaitis Eratosthenes (ehr-uh-TAHS-thuh-neez) Eratosthenes was a Greek mathematician, astronomer, and geographer. He invented a method for finding prime numbers that is still used today. This method is called Eratosthenes Sieve.

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Copyright © 2000 by Monica Yuskaitis Eratosthenes Sieve A sieve has holes in it and is used to filter out the juice. Eratostheness sieve filters out numbers to find the prime numbers.

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Copyright © 2000 by Monica Yuskaitis Definition Factor – a number that is multiplied by another to give a product. 7 x 8 = 56 Factors

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Copyright © 2000 by Monica Yuskaitis Definition Factor – a number that divides evenly into another. 56 ÷ 8 = 7 Factor

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Copyright © 2000 by Monica Yuskaitis Definition Prime Number – a number that has only two factors, itself and is prime because the only numbers that will divide into it evenly are 1 and 7.

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Copyright © 2000 by Monica Yuskaitis Hundreds Chart On graph paper, make a chart of the numbers from 1 to 100, with 10 numbers in each row.

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Copyright © 2000 by Monica Yuskaitis Hundreds Chart

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Copyright © 2000 by Monica Yuskaitis – Cross out 1; it is not prime.

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Copyright © 2000 by Monica Yuskaitis Hint For Next Step Remember all numbers divisible by 2 are even numbers.

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Copyright © 2000 by Monica Yuskaitis – Leave 2; cross out multiples of 2

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Copyright © 2000 by Monica Yuskaitis Hint For Next Step To find multiples of 3, add the digits of a number; see if you can divide this number evenly by 3; then the number is a multiple of Total of digits = 15 3 divides evenly into is a multiple of 3

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Copyright © 2000 by Monica Yuskaitis – Leave 3; cross out multiples of 3

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Copyright © 2000 by Monica Yuskaitis To find the multiples of 5 look for numbers that end with the digit 0 and 5. Hint For the Next Step 385 is a multiple of 5 & 890 is a multiple of 5 because the last digit ends with 0 or 5.

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Copyright © 2000 by Monica Yuskaitis – Leave 5; cross out multiples of 5

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Copyright © 2000 by Monica Yuskaitis – Leave 7; cross out multiples of 7

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Copyright © 2000 by Monica Yuskaitis –Leave 11; cross out multiples of 11

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Copyright © 2000 by Monica Yuskaitis All the numbers left are prime

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Copyright © 2000 by Monica Yuskaitis The Prime Numbers from 1 to 100 are as follows: 2,3,5,7,11,13,17,19, 23,31,37,41,43,47, 53,59,61,67,71,73, 79,83,89,97

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Copyright © 2000 by Monica Yuskaitis Credits Clipart from Microsoft Clip Gallery located on the Internet at clipgallerylive/default.asp

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