# What is NUMBER SYSTEM?

General Question from Number System for points to remember

**Points To Remember**

**Natural Numbers:**Counting numbers are known as natural numbers. e.g. 1,2,3,… .**Whole Numbers:**All natural numbers together with 0 form whole numbers. e.g. 0,1,2,3…**Odd Numbers:**A number not divisible by 2 is called odd number. g. 1, 3, 5, 7, 9,….etc.**Even Numbers:**A number divisible by 2 is called even number. g. 2, 4, 6, 8,……etc.**Prime Numbers:**Natural numbers which are divisible only by 1 and the number itself are called prime numbers.

e.g. 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47,…. etc.

**Composite Numbers:**The numbers which has more than two factors, except the number 1 and the number itself are known as composite numbers. g. 4, 6, 8, 9, 10, 12, 14, 15,…etc.

**Note: **

(i) ‘1’ is neither prime nor composite (ii) ‘2’ is the only even prime.

**Co-prime Numbers:**Two natural numbers (not necessarily prime) are co-prime, if their H.C.F. (Highest common factor) is one.

e.g. (1, 2), (1, 3), (3, 4), (3, 10), (3, 8), (5, 6), etc.

**Integers:**All natural numbers, 0 and the negatives of natural numbers form the collection of integers. e.g. – ¥…-4, -3, -2, -1, 0, 1, 2, 3,….+infinty.

**Rational Numbers:**The numbers of the form where p and q are integers and q ¹ 0 are known as rational numbers. e.g. 0, all natural numbers, all integers,, …. etc.

Decimal representation of rational numbers is terminating or non-terminating but repeating.

**Irrational Numbers:**The numbers which cannot be expressed in the form , where p and q are integers and q ¹ 0 are known as irrational numbers e.g. 020020002 … etc.

Decimal representation is non-terminating and non-repeating.

**Real Numbers:**The collection of rational and irrational numbers are real numbers and is denoted by R.