Sieve of Eratosthenes
ANSWER KEY
XOOXOXOX X
X X X X X
X X X X X
X X X X X
X X X X X
X X X X X
X X X X X
X X X X X
X X X X X
X X X X X
X
1 2 3 4 5 X
6 7 8 X
9 10
11 12
X 16 1718
X 15
X 19 20
X
X 13 14
X
X
21
X 29 30
X
X 27
X 28
X 2526
X
X 22 23 24
31 32 33
X
XX X 37 38 39
X 34 3536
X 40
X
41 42
XX43 44 45
X 49
X 50
XX 46 47 48
51
X
60
X 57
X 56
X 55
X 52 53 54
X 58 59 X
XX
61 62 63
X 66
X 67 68 69
XX64 65
X 70
X
79
80
71 72
X 76 77
X 73 74 75
X 78
X
X
81
90
X 82 83 84
X 88 89 X
X 86 87
XX 85
X
91
X 92 93
X 97 98
X 96
X 94 95
X 99
X 100
1. Cross out 1 with a black
pencil.
2. Circle 2 with a purple
colored pencil.
3. Cross out multiples of 2 (skip
count by 2) with the purple
colored pencil.
4. Circle 3 with a red colored
pencil.
5. Cross out multiples of 3 with
the red colored pencil.
6. Circle 5 with a green colored
pencil.
7. Cross out multiples of 5 with
the green colored pencil.
8. Circle 7 with a blue colored
pencil.
9. Cross out multiples of 7 with
the blue colored pencil.
10.Continue to the next page.
Sieve of Eratosthenes
name: ___________________________date: ________________________
1 2 3 4 5 6 7 8 9 10
11 12 13 14 15 16 1718 19 20
21 22 23 24 2526 27 28 29 30
31 32 33 34 35 36 37 38 39 40
41 42 43 44 45 46 47 48 49 50
51 52 53 54 55 56 57 58 59 60
61 62 63 64 65 66 67 68 69 70
71 72 73 74 75 76 77 78 79 80
81 82 83 84 85 86 87 88 89 90
91 92 93 94 95 96 97 98 99 100
1. Cross out 1.
2. Circle 2 with a purple
colored pencil.
3. Cross out multiples of 2 (skip
count by 2) with the purple
colored pencil.
4. Circle 3 with a red colored
pencil.
5. Cross out multiples of 3 with
the red colored pencil.
6. Circle 5 with a green colored
pencil.
7. Cross out multiples of 5 with
the green colored pencil.
8. Circle 7 with a blue colored
pencil.
9. Cross out multiples of 7 with
the blue colored pencil.
10.Continue to the next page.
Questions
1. Check: How many uncrossed out numbers do you have (they can be circled)? If you don't
have 25 uncrossed out numbers, check your work. ______________________________
2. Is one prime or composit? Explain why (or why not).
________________________________________________________________________
________________________________________________________________________
3. Are the uncrossed off numbers prime or composite? Explain how you know this.
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
4. Why didn't we cross off any numbers after the multiples of 7?
________________________________________________________________________
________________________________________________________________________
5. Describe how we know that a number is prime.
________________________________________________________________________
________________________________________________________________________
6. Describe how we know that a number is composite.
________________________________________________________________________
________________________________________________________________________
7. List three things that you notice about your 100s chart after crossing off the composite
numbers.
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
Check one: This was HARD _________ OK _________ EASY _________