Page 65 - Math Genius C5

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\\October 8, 2025 12:13 PM Bharat Arora P-9 Reader _________________________ Date: ___________________74

We can observe from the table:
Š 2, 3, 5 and 7 have exactly two factors.

Š 4, 6, 8, 9 and 10 have more than two factors.

The numbers which have only two factors, 1 and the number itself, are called prime numbers

and the numbers which have more than two factors are called composite numbers.
Let us find prime and composite numbers between 1 and 100. Math Insight

A Greek mathematician, Eratosthenes, developed an The number 1 is a unique
interesting and simple method for finding prime numbers number. It is neither prime
nor composite.
which is called the Sieve of eratosthenes.

activity Experiential Learning
Step 1: Take a chart paper

and make a 10 × 1 2 3 4 5 6 7 8 9 10
10 grid and write
numbers from 1 to 11 12 13 14 15 16 17 18 19 20
100 in it. 21 22 23 24 25 26 27 28 29 30
Step 2: Enclose 1 in a box as 31 32 33 34 35 36 37 38 39 40
it is a unique number.

Step 3: Circle the number 2 41 42 43 44 45 46 47 48 49 50
and cross out all its 51 52 53 54 55 56 57 58 59 60
multiples. 61 62 63 64 65 66 67 68 69 70

Step 4: Circle 3 and cross
out all its multiples. 71 72 73 74 75 76 77 78 79 80
(Some multiples of 3 81 82 83 84 85 86 87 88 89 90
may be crossed out 91 92 93 94 95 96 97 98 99 100
as multiples of 2.)
Step 5: Circle 5 and cross out all its multiples.

Step 6: Circle 7 and cross out all its multiples.
Step 7: Continue this process till all the numbers are either crossed out or circled.

All the circled numbers are prime numbers and all the crossed-out numbers are composite
numbers.

The prime numbers between 1 and 100 are 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41,
43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89 and 97.

Š 2 is the smallest and only even prime number. Think Tank Logical Thinking
Is your roll number a prime
Š 4 is the smallest composite number. number? Check.

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