Sieve of Eratosthenes.

http://www.mathslideshows.com Sieve of Eratosthenes

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 the Sieve of Eratosthenes. Eratosthenes (ehr-uh-tahs-thuh-neez)

http://www.mathslideshows.com Sieve of Eratosthenes 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.

http://www.mathslideshows.com FACTOR A Factor is a number that is multiplied by another number to give the product. 7 x 8 = 56 Factors

http://www.mathslideshows.com FACTOR A Factor is the number that divides evenly into another. 56 ÷ 8 = 7 Factor

http://www.mathslideshows.com PRIME NUMBER A Prime Number is 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.

http://www.mathslideshows.com Hundreds Chart I am going to give you a hundreds chart with the numbers from 1 to 100, with 10 numbers in each row. You are going to use the Sieve of Eratosthenes to discover the prime numbers between 1 and 100.

http://www.mathslideshows.com 12345678910 11121314151617181920 21222324252627282930 31323334353637383940 41424344454647484950 51525354555657585960 61626364656667686970 71727374757677787980 81828384858687888990 919293949596979899 100 Hundreds Chart

http://www.mathslideshows.com 12345678910 11121314151617181920 21222324252627282930 31323334353637383940 41424344454647484950 51525354555657585960 61626364656667686970 71727374757677787980 81828384858687888990 919293949596979899 100 1 – Cross out 1; it is NOT prime.

http://www.mathslideshows.com Hint For Next Step Remember all numbers divisible by 2 are even numbers. Remember they end in 0, 2, 4, 6, 8…

http://www.mathslideshows.com 12345678910 11121314151617181920 21222324252627282930 31323334353637383940 41424344454647484950 51525354555657585960 61626364656667686970 71727374757677787980 81828384858687888990 919293949596979899 100 2 – Leave 2; Cross out multiples of 2

http://www.mathslideshows.com Hint For Next Step To find multiples of 3, add the digits of a number. If the sum divides evenly by 3 then the number is a multiple of 3. 2 6 7 Add the digits: 2 + 6 + 7 = 15 15 is divisible by 3 so 267 is a multiple of 3

http://www.mathslideshows.com Hint For the Next Step Remember the number 4 is a multiple of 2 a nd an even number. You don’t have to do multiples of 4 since you already crossed off multiples of 2.

http://www.mathslideshows.com To find the multiples of 5 look for numbers that end with the digit 0 and 5.5. Hint For the Next Step 385 is a multiple of 5 and 890 is a multiple of 5 because the last digit ends with 0 or 5.

http://www.mathslideshows.com Hint For the Next Step Remember a number is divisible by 6 if it is divisible by 2 and 3. Since you have already crossed out multiples of 2 and 3 then you have already done multiples of 6.

http://www.mathslideshows.com Hint For the Next Step Remember the number 8 is a multiple of 2, the number 9 is a multiple of 3, and the number 10 is a multiple of 2.2. What number do you think is next?

http://www.mathslideshows.com 12345678910 11121314151617181920 21222324252627282930 31323334353637383940 41424344454647484950 51525354555657585960 61626364656667686970 71727374757677787980 81828384858687888990 919293949596979899 100 The leftover numbers are prime numbers.

http://www.mathslideshows.com 12345678910 11121314151617181920 21222324252627282930 31323334353637383940 41424344454647484950 51525354555657585960 61626364656667686970 71727374757677787980 81828384858687888990 919293949596979899 100 Circle the rest of the primes on your chart.

http://www.mathslideshows.com The Prime Numbers from 1 to 100 are as follows: Write these down on the bottom of your paper: 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 A prime number is a number that has no factors other than 1 and itself. There are 25 prime numbers from 0 to 100. Check your list to make sure you have them all!

http://www.mathslideshows.com Composite numbers have more than 2 factors. PRIME FACTORIZATION is the unique set of prime numbers whose product equals a given number. Write the prime factorization for the following. 24 Factor Tree 2 12 2 6 4 6 2 3 2 2 2 3

http://www.mathslideshows.com Take Out Your Study Guide!!!

http://www.mathslideshows.com FACTOR A Factor is a number that is multiplied by another number to give the product. 7 x 8 = 56 Factors A Factor is the number that divides evenly into another number. 56 ÷ 8 = 7 Factor #3

http://www.mathslideshows.com Prime Numbers- A Prime number is a whole number with exactly 2 factors, one and itself. Example: 17, 3, 2, 11, 13, 5 Composite Numbers- A Composite number is a number that has more than two factors. Example: 9, 30, 64, 8, 40, 69 #4 Prime & Composite

http://www.mathslideshows.com Teacher Note : Use the next slide as a master. Make one copy for each student to use to do this interactive lesson on discovering prime numbers

12345678910 11121314151617181920 21222324252627282930 31323334353637383940 41424344454647484950 51525354555657585960 61626364656667686970 71727374757677787980 81828384858687888990 919293949596979899 100 Hundreds Chart

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