Page 83 - ICSE Math 4

Prime and Composite Numbers between 1 and 100

Top Tip
1 11 21 31 41 51 61 71 81 91
Prime numbers that
2 122232425262728292 diff er by 2 are known as twin
3 132333435363738393 prime numbers. For example,
3 and 5; 5 and 7; 11 and 13
4 142434445464748494 and so on.
5 152535455565758595

6 162636465666768696 neither prime nor

7 172737475767778797 composite number
8 182838485868788898 Prime numbers

9 192939495969798999
Composite
10 20 30 40 50 60 70 80 90 100

To fi nd out whether the given number is a prime number or a composite number, we

follow the given steps.
• Find all the factors of the given number.

• If the number has only two factors, i.e., 1 and the number itself, then it is a prime
number.

• If the number has more than two factors, then it is a composite number.
Example 8: Find out whether 7, 19, 27 and 35 are prime or composite numbers.

Solu on: Write all the factors of the given numbers.

7 = 1 × 7 Factors of 7 are 1 and 7.

19 = 1 × 19 Factors of 19 are 1 and 19.

27 = 1 × 27 and 3 × 9 Factors of 27 are 1, 3, 9 and 27.

35 = 1 × 35 and 5 × 7 Factors of 35 are 1, 5, 7 and 35.
The numbers 7 and 19 have only two factors. Remember
So, they are prime numbers. 0 and 1 are neither

The numbers 27 and 35 have more than two prime nor composite
numbers.
factors. So, they are composite numbers.

Prime Factors

A prime factor is a prime number that divides the given number exactly. When the prime
numbers are mul plied, they give the original number.

Every composite number can be wri en as a product of factors that are prime numbers.

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