Page 175 - Demo

174 Arrow-Puffin-4_Semester-1 MathsThere are 26 prime numbers between 1 and 100.This method of finding prime numbers between 1 and 100 was found by a Greek mathematician named Eratosthenes. This method is popularly known as the Sieve of Eratosthenes.Finding Prime Numbers Between 1 and 100Write all the numbers from 1 to 100 in a tabular form as shown.1 2 3 4 5 6 7 8 9 1011 12 13 14 15 16 17 18 19 2021 22 23 24 25 26 27 28 29 3031 32 33 34 35 36 37 38 39 4041 42 43 44 45 46 47 48 49 5051 52 53 54 55 56 57 58 59 6061 62 63 64 65 66 67 68 69 7071 72 73 74 75 76 77 78 79 8081 82 83 84 85 86 87 88 89 9091 92 93 94 95 96 97 98 99 100Step 1 : Cross 1 since 1 is not a prime number.Step 2 : Since 2 x 1 = 2. So, 2 is a prime number.Similarly 3 x 1 = 3 5 x 1 = 5 7 x 1 = 72, 3, 5, 7 all are prime numbers. So, circle all these numbers.Step 3 : Cross all the multiples of 2, 3, 5 and 7.Step 4 : After crossing all the multiples of 2, 3, 5 and 7, circle the remaining numbers. All the circled numbers are prime numbers between 1 and 100.Composite NumbersA number that has more than two factors is called a composite number. Examples : 4 is a composite number as factors of 4 are 1, 2 and 4. 6 is a composite number as factors of 6 are 1, 2, 3 and 6.