PRIME NUMBERS
Prime Numbers are special whole numbers that only have TWO FACTORS.
Factors are the numbers that, when multiplied, give you a product.
For example:
3 x 1 = 3 (So the factors of 3 are: 3 and 1) ==> There are only two factors
5 x 1 = 5 (So the factors of 5 are: 5 and 1) ==> There are only two factors
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Composite Numbers are special whole numbers that MORE THAN TWO FACTORS.
Factors are the numbers that, when multiplied, give you a product.
For example:
9 x 1 = 9 (So the factors of 9 are 1, 3, 9) ==> There are three factors
3 x 3 = 9
8 x 1 = 8 (So the factors of 8 are 1, 2, 4, 8) ==> There are four factors
2 x 4= 8
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So either a whole number is prime or it is composite. Look at the numbers 1 to 33
Numbers in RED are PRIME. Numbers in BLACK are COMPOSITE.
THE NUMBER 1 IS IN GREEN - IT IS NOT A PRIME NUMBER, NOR A COMPOSITE NUMBER.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
19 20 21 22 23 24 25 26 27 28 29 30 31 32 33
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Which Prime Numbers (in red) are EVEN? - Do you notice there is only ONE?
Factors are the numbers that, when multiplied, give you a product.
For example:
3 x 1 = 3 (So the factors of 3 are: 3 and 1) ==> There are only two factors
5 x 1 = 5 (So the factors of 5 are: 5 and 1) ==> There are only two factors
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Composite Numbers are special whole numbers that MORE THAN TWO FACTORS.
Factors are the numbers that, when multiplied, give you a product.
For example:
9 x 1 = 9 (So the factors of 9 are 1, 3, 9) ==> There are three factors
3 x 3 = 9
8 x 1 = 8 (So the factors of 8 are 1, 2, 4, 8) ==> There are four factors
2 x 4= 8
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So either a whole number is prime or it is composite. Look at the numbers 1 to 33
Numbers in RED are PRIME. Numbers in BLACK are COMPOSITE.
THE NUMBER 1 IS IN GREEN - IT IS NOT A PRIME NUMBER, NOR A COMPOSITE NUMBER.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
19 20 21 22 23 24 25 26 27 28 29 30 31 32 33
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Which Prime Numbers (in red) are EVEN? - Do you notice there is only ONE?
ACTIVITIES
HOW TO DETERMINE PRIME NUMBERS?
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You can determine the prime numbers between 1 and 100 by using the experiment called the 'Sieve of Eratosthenes'. This involves crossing off all numbers with MORE THAN 2 FACTORS in a methodical way.
We are going to LEAVE the numbers that only have 2 factors UNSHADED. Then we are going to shade ALL MULTIPLES of the prime numbers we know between 2 and 7. When we are done, all of the UNSHADED numbers are Prime Numbers. Download and PRINT the GRID to follow along and watch the MAGIC: 1. Since 1 is not Prime, leave it shaded. 2. Since '2' is the ONLY EVEN prime number, LEAVE IT UNSHADED. Then SHADE ALL MULTIPLES OF 2. 3. Since '3' is a prime number, LEAVE IT UNSHADED. Then SHADE ALL MULTIPLES OF 3. 4. Since '5' is the ONLY EVEN prime number, LEAVE IT UNSHADED. Then SHADE ALL MULTIPLES OF 5. 5. Since '7' is the ONLY EVEN prime number, LEAVE IT UNSHADED. Then SHADE ALL MULTIPLES OF 7. 6. All UNSHADED numbers are PRIME NUMBERS! |
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