Composite Numbers
 

A Composite number is a whole number that can be divided evenly by a number other than itself or 1.    Examples:   
2 =   1 x 2    Not Composite
3 =   1 x 3    Not Composite
4 =   1 x 4, 2 x 2     Composite
5 =   1 x 5    Not Composite
6 =   1 x 6, 2 x 3     Composite
7 =   1 x 7    Not Composite
8 =   1 x 8, 2 x 4     Composite
9 =   1 x 9, 3 x 3     Composite

 

The  "Sieve of Eratosthenes"  can be used to show numbers that are composite numbers.   To use the little sieve below:

Click the requests to remove the multiples of 2,3,5,7,and 11 on the left side of the table.   What remains will be the prime numbers less than 100.

The removed numbers are the composite numbers that are less than 100.

 
 

 

 Remove multiples of 2, except 2.

1 2 3 4 5 6 7 8 9 10
11 12 13 14 15 16 17 18 19 20

Remove multiples of 3, except 3.

21 22 23 24 25 26 27 28 29 30
31 32 33 34 35 36 37 38 39 40

Remove multiples of 5, except 5.

41 42 43 44 45 46 47 48 49 50
51 52 53 54 55 56 57 58 59 60

Remove multiples of 7, except 7.

61 62 63 64 65 66 67 68 69 70
71 72 73 74 75 76 77 78 79 80

Remove multiples of 11, except 11.

81 82 83 84 85 86 87 88 89 90
91 92 93 94 95 96 97 98 99 100

 

                

Check Your Understanding

  1. Think of a composite number between 2 and 100.
  2. Enter the number below.
  3. Click the button "Check" and check your answer.
Number:

Answer: