1. Prime NumbersEratosthenes’ Sieve By Monica Yuskaitis

2. 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.

3. 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.

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

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

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

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

8. 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.

9. Copyright © 2000 by Monica Yuskaitis Hundreds Chart

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

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

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

13. 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 3. 2 6 7 Total of digits = 15 3 divides evenly into 15 267 is a multiple of 3

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

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

16. Copyright © 2000 by Monica Yuskaitis 4– Leave 5; cross out multiples of 5

17. Copyright © 2000 by Monica Yuskaitis 5– Leave 7; cross out multiples of 7

18. Copyright © 2000 by Monica Yuskaitis 6–Leave 11; cross out multiples of 11

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

20. Copyright © 2000 by Monica Yuskaitis The Prime Numbers from 1 to 100 are as follows: 2,3,5,7,11,13,17,19, 23,29,31,37,41,43,47, 53,59,61,67,71,73, 79,83,89,97

21. Copyright © 2000 by Monica Yuskaitis Credits Clipart from “Microsoft Clip Gallery” located on the Internet at http://cgl.microsoft.com/ clipgallerylive/default.asp