Page 53 - Maths Class 05
P. 53
Prime Numbers and Composite Numbers
All prime numbers have only one rectangular array.
2
1
1 × 2 = 2
This means a prime number has only two
3 factors, 1 and the number itself.
1 × 3 = 3
Now, look at the following.
Prime Numbers between 1 and 100
A greek mathematician, Eratosthenes, about 230 BC, developed the method of finding
prime numbers between 1 to 100. This method gives us a grid, known as sieve of
Eratosthenes.
Method : Write down the numbers from 1 to 100 as shown below.
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
Ü Cross 1, as it is neither prime nor composite.
Ü Leave 2 as it is a prime number but circle all the multiples of 2.
Ü Leave 3 as it is a prime number, but circle all its multiples.
Mathematics-5 53
