Name
Prime Numbers and Composite Numbers
Let's learn about two new terms-Prime Numbers and Composite Numbers.
A prime number is only divisible by 1 and itself.
Example: 3 is a prime number.
A prime number will have only two factors, 1 and the number itself.
Example: 5, 7, 11, 13, are all Prime Numbers.
Work it out...
Which of these are prime numbers? Circle them.
11
15
5
13
7
10
9
12
Related is the term composite numbers. Numbers which have more than two
factors are called composite numbers.
Example: 10, 12, 24, 36, are all composite numbers.
Work it out...
Which of these are composite numbers? Circle them.
48
32
112
81
3
4
11
12
FUN FACTS:
A 1 is Neither prime nor composite.
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e plore
b 2 is the only even prime number.
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Prime Numbers from 1 to 100
Long ago, a Greek mathematician named Eratosthenes found a method to
identify the prime numbers from 1 to 100.
Look at the following Number Grid:
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
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
Cross out 1. It is not a prime number
Leave 2, since it is prime. But cross out all the multiples of 2.
Leave 3, since it is prime. But cross out all the multiples of 3.
Leave 5, since it is prime. But cross out all the multiples of 5.
Leave 7, since it is also prime. But cross out all the multiples of 7.
List all the numbers that are not crossed out.
These are all the prime numbers from 1 to 100.
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e plore
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Work it out...
A How many prime numbers are there between 1 and 100?
b State the smallest and largest prime number in the List?
Smallest
Largest
c Identify the prime numbers between 90 and 100.
d How many prime numbers have 3 in the Ones digit?
Do your calculations here.
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e plore
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