Name:
Date :
Grade 8 Math: Prime Numbers
1. A ​prime​ number is: ______________________________________________________
2. A ​composite ​number is: ___________________________________________________
_______________________________________________________________________
3. How many distinct factors does the number 1 have?
4. Is 1 a prime number?
5. Is 1 a composite number?
6. List all prime numbers less that 10.
______________________________________________________________________
7. List all composite numbers between 1 and 20.
______________________________________________________________________
8. What is the greatest prime number less than 20?
9. Circle the prime numbers in each list.
a)
5
4
2
8
9
1
b) 6
2
3
4
7
10
c) 11 25
14
13
17
20
d) 27 15 12
18
29
33
10. Write a number between 0 and 20 that has:
a) 2 factors
b) four factors
c) five factors
11. The primes numbers 3 and 5 differ by 2. Find three other pairs of prime numbers less than
20 that differ by 2.
12. Write three consecutive numbers which are also all composite numbers.
1
Grade 8
Prime Numbers
● Eratosthenes's Sieve.
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 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 78 80
81 82 83 84 85 86 87 88 89 90
91 92 93 94 95 96 97 98 99 100
Directions:
1. Shade the number 1.
2. Circle 2, 3, 5 and 7 (primes less than 10).
3. Shade all the remaining multiples of 2.
4. Shade all the remaining multiples of 3.
5. Shade all the remaining multiples of 5.
6. Shade all the remaining multiples of 7.
7. Circle the next uncircled number (11).
Q. How do you know all multiples of this number has been shaded?
8. Circle all the remaining numbers.
2
Grade 8
Prime Numbers
Looking at your Eratosthenes’ Sieve chart answer the following questions.
1. List all prime numbers between 30 and 70.
2. How many primes numbers between 1 and 100?
3. How many composite numbers between 80 and 100?
4. Solve these riddle. (Solve each part independently).
What number am i?
a) I am a prime number less than 100. If you add 10 or 20 to me, the result is prime.
b) I am a prime number less than 100. My digits add to 13.
c) I am a prime number less than 100. My tens digit is one than my ones digit.
d) I am a prime number between 20 and 70. If you reverse my digits, the result is a larger
larger prime number.
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