Category : 3rd Class
Introduction Numbers are useful in counting quantities that we see around us in our daily life. The numbers that we use our country is the Hindu - Arabic numerals. Aryabhatta developed the place value of Hindu Arabic numerals and Brahmagupta introduced the symbol for zero. Hindu Arabic numerals were basically developed in India and laterally accepted by Arabians so called Hindu Arabic numerals. In this chapter we will learn about Hindu - Arabic numbers and their comparison with Roman and International number system. Natural Numbers Counting numbers are known as natural numbers. There are infinite natural numbers starting from 1. Natural number is denoted by N. 
Which one of the following numbers is not a natural number? (a) -3 (b) 3 (c) 2 (d) 50 (e) None of these Answer (a) 
Whole Numbers The counting numbers including 0 are known as whole numbers. If counting numbers start from 0 then they include the set of whole numbers. Whole number is denoted by W. Prime Numbers The number which has only two factors, 1 and the number itself is called prime number. The number 2 does not have the factors other than 1 therefore, 2 is a prime number. 2 is only from the group of even numbers which has only two factors, so it is called even prime number. Look at the following table of prime numbers between 1 and 100:
| 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 |
Highlighted numbers are prime numbers. Even Numbers The numbers those are exactly divisible by 2 are called even numbers. The numbers 2, 4, 6, 8, 10.... etc. are even numbers. Consider the following two statements: Statement 1: The division of two even numbers is always an even number. Statement 2: The division of an even number by 2 always leaves 0 remainder. Which one of the following options is correct about the above statements? (a) Statement 1 is true and 2 is false (b) Statement 1 is false and 2 is true (c) Both statements 1 and 2 are false (d) All of these (e) None of these Answer (b) Explanations Division of two even numbers is not always an even number. Division of an even number by 2 always leaves 0 as a remainder. Odd Numbers The numbers which are not divisible by 2 are called odd numbers. Odd numbers do not come in the table of 2. The numbers 1, 3, 5, 7, 9......... etc. are odd numbers. How many odd numbers are there from 1 to 10? (a) 2 (b) 3 (c) 5 (d) 9 (e) None of these Answer (c) Twin Primes Two prime numbers having a difference of 2 are called twin primes. The difference of the prime numbers 3 and 5 is 2, therefore, they are called twin primes. Twin primes. 3 and 5, 5 and 7, 11 and 13, 17 and 19, etc are. 
There are four prime numbers between 1 and 10 and again four prime numbers between 11 and 20. How many prime numbers are there between 91 and 100? (a) 1 (b) 3 (c) 5 (d) All of these (e) None of these Answer (a) Explanation The numbers from 91 to 100 are 92, 93, 94, 95, 96, 97, 98, 99. The number 97 has two factors 1 and the 97 itself. Hence, 97 is the only prime number between 91 and 100. Composite Numbers The numbers which have more than two factors other than 1 and the number itself are called composite numbers. Even numbers except 2 are composite numbers. Composite Numbers between 1 and 100
