Download prime numbers

Number
N1/L2.2
PRIME NUMBERS
If a number only has 1 and itself as a factor, we call it a prime number.
e.g.
The only factors of 13 are 1 and 13, so 13 is a prime factor.
1 is not a prime number
A.
Have a go at these
1)
Find the factors of all the numbers from 2 to 10. Which
numbers are prime numbers?
2)
Follow the instructions below to find all the prime numbers up to
100.
(a)
Look through the number square on the next page. Go
through and cross out all the numbers in your 2 times table
up to 100.
(b)
Next cross out all the numbers in your 3 times table.
(c)
Go through all your times tables up to your 10 times.
REMEMBER you MUST go up to 100 with each one.
The numbers that are left are the prime numbers.
(d)
Write a list of all the prime numbers from 2 to 100.
Remember to include the numbers less than 10 you
to be prime. There should be 25 numbers
altogether.
1
found
Number
N1/L2.2
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
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67
68
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70
71
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73
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100
Prime Factors
The prime factors of a number are exactly what it says, factors that are
also prime numbers.
Examples
(a)
Find the prime factors of 15.
The factors are 1, 3, 5 and 15. The prime factors are 3 and 5 because
they are also prime numbers.
2
Number
N1/L2.2
(b)
Find the prime factors of 12.
The factors are 1, 2, 3, 6 and 12.
2 and 3 are prime factors.
(c)
Find the prime factors of 6.
Factors are 1, 2, 3, 6
2 and 3 are prime factors
Make sure you understand the examples.
B.
Find the prime factors of each of the following
numbers.
1)
8
2)
18
4)
36
5)
24
3)
25
Check your answers, then discuss with your tutor what you need to
work on next.
3
Number
N1/L2.2
Answers
Prime Numbers
A
1) 2 —
1, 2
3—
1, 3
4—
1, 2, 4
5—
1, 5
6—
1, 2, 3, 6
7—
1, 7
8—
1, 2, 4, 8
9—
1, 3, 9
10 —
1, 2, 5, 10
The prime numbers are:
2, 3, 5 and 7
2) 2, 3, 5, 7, 11, 13, 17, 19, 23,
29, 31, 37, 41, 43, 47, 53,
59, 61, 67, 71, 73, 79, 83, 89, 97
B
1) 2
2)
2 and 3
4) 2 and 3
5)
2 and 3
4
3)
5