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Prime Numbers Eratosthenes’ Sieve

Prime Numbers Eratosthenes’ Sieve. By www.2july.co.uk. Eratosthenes (ehr-uh-TAHS-thuh-neez). Eratosthenes was the librarian at Alexandria, Egypt in 200 B.C. . Eratosthenes (ehr-uh-TAHS-thuh-neez). Eratosthenes was a Greek mathematician, astronomer, and geographer.

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Prime Numbers Eratosthenes’ Sieve

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  1. Prime NumbersEratosthenes’ Sieve By www.2july.co.uk

  2. Eratosthenes(ehr-uh-TAHS-thuh-neez) Eratosthenes was the librarian at Alexandria, Egypt in 200 B.C.

  3. 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. Eratosthenes’ Sieve • A sieve has holes in it and is used to filter out liquids from solids. • Eratosthenes’s sieve filters out numbers to find the prime numbers.

  5. Definition • A Factor – a number that is multiplied by another to give a product. 7 x 8 = 56 Factors

  6. Definition • A Factor – a number that divides exactly into another. 56 ÷ 8 = 7 Factor

  7. Definition • A Prime Number – a number that has only two factors, itself and 1. 1 x 7 = 7 7 is prime because the only numbers that will divide into it evenly are 1 and 7. Note: 1 is not a PRIME as it only has 1 factor repeated, 1x1 = 1

  8. Hundreds Chart • On graph paper, make a chart of the numbers from 1 to 100, with 10 numbers in each row.

  9. A Hundreds Chart

  10. 1 – Cross out 1; it is not prime.

  11. Hint For Next Step • Remember all numbers divisible by 2 are even numbers.

  12. 2 – Leave 2; cross out multiples of 2

  13. 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. 3– Leave 3; cross out multiples of 3

  15. 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. 4– Leave 5; cross out multiples of 5

  17. 5– Leave 7; cross out multiples of 7

  18. 6–Leave 11; cross out multiples of 11

  19. All the numbers left are prime

  20. 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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