In this article, we will cover the CSIR NET General Aptitude Most Important Formulas of Number System. Aspiring candidates can check all the most important formulas of the Number System for the last-minute revision. Scroll down the full article to find out!

**Formula Sheet On Number System**

The number system is an important topic for upcoming Exams. Here, we are going to help you with Basic Concepts & Short Tricks on Number Systems in Quant Section. We will be providing you with details of the topic to make the Quant Section and calculation easier for you all to understand. The number system is an important topic for upcoming Exams. Here, we are going to help you with Basic Concepts & Short Tricks on Number Systems in Quant Section. We will be providing you with details of the topic to make the Quant Section and calculation easier for you all to understand.

(1) **Natural Numbers**: Numbers starting from 1, 2, 3 and so on so forth are counted as Natural numbers. They are 1, 2, 3, 4...Exceptions: Zero, negative and decimal numbers are not counted in this list.

(2) **Whole numbers**: Zero and all other natural numbers are known as natural numbers. They are 0, 1, 2, 3, 4...

(3)** Integers**: They are the numbers that include all the whole numbers and their negatives. They are ...-4, -3, -2, -1, 0, 1, 2, 3, 4....

(4) **Rational Numbers**: All the numbers which are terminating, repeating and can be written in the form p/q, where p and q are integers and q should not be equal to 0 are termed as rational numbers.Example: 0.12121212...

(5) **Irrational Numbers**: All the numbers which are non-terminating, non-repeating and cannot be written in the form p/q, where p and q are integers and q should not be equal to 0 are termed as irrational numbers.Example: pie, e

(6) **Real numbers**: All the numbers existing on the number line are real numbers. The group is made up of all rational and irrational numbers.

(7) **Imaginary Numbers**: Imaginary numbers are the numbers formed by the product of real numbers and imaginary unit 'i'. This imaginary unit is defined as the following:i2= -1, multiplication of this 'i' is calculated according to the above value. Example: 8i

(8) **Complex Number**: The numbers formed by the combination of real numbers and imaginary numbers are called complex numbers. Every complex number is written in the following form: A+iB, where A is the real part of the number and B is the imaginary part.

(9) **Prime numbers**: All the numbers having only two divisors, 1 and the number itself is called a prime number. Hence, a prime number can be written as the product of the number itself and 1. Example: 2, 3, 5, 7 etc.

(10) **Composite Numbers**: All the numbers which are not prime are called composite numbers. This number has factors other than one and itself.Example: 4, 10, 99, 105, 1782 etc.

(11) **Even & Odd Numbers**: All the numbers divided by 2 are even numbers. Whereas the ones not divisible by 2 are odd numbers.Example: 4, 6, 64, 100, 10004 etc. are all even numbers.3, 7, 11, 91, 99, 1003 are all odd numbers.

(12) **Relative Prime Numbers/Co-prime Numbers**: Numbers that do not have any common factor other than 1 are called co-prime numbers.Example: 5 and 17 are co-primes.

(13) **Perfect Numbers**: All the numbers are called perfect numbers if the sum of all the factors of that number, excluding the number itself and including 1, equalizes the to the number itself then the number is termed as a perfect number. Example:6 is a perfect number. As the factors of 6= 2 and 3. As per the rule of perfect numbers, sum= 2+3+1 = 6. Hence, 6 is a perfect number.

**Some important properties of Numbers:**

1. The number 1 is neither prime nor composite.

2. The only number which is even is 2.

3. All the prime numbers greater than 3 can be written in the form of (6k+1) or (6k-1) where k is an integer.

4. Square of every natural number can be written in the form 3n or (3n+1) and 4n or (4n+1).

5. The tens digit of every perfect square is even unless the square is ending in 6 in which case the tens digit is odd.

6. The product of n consecutive natural numbers is always divisible by n! where n!= 1X2X3X4X….Xn (known as factorial n).

To test whether a given number is a prime number or not

If you want to test whether any number is a prime number or not, take an integer larger than the approximate square root of that number. Let it be ‘x’. test the divisibility of the given number by every prime number less than ‘x’. if it is not divisible by any of them then it is a prime number; otherwise, it is a composite number (other than prime).**Example**: Is 349 a prime number?**Solution:**

The square root of 349 is approximate 19. The prime numbers less than 19 are 2, 3, 5, 7, 11, 13, 17.

Clearly, 349 is not divisible by any of them. Therefore, 349 is a prime number.

**Rules of Simplification**

(i) In simplifying an expression, first of all, the vinculum or bar must be removed. For example we have known that – 8 – 10 = -18

(ii) After removing the bar, the brackets must be removed, strictly in the order (), {} and [].

(iii) After removing the brackets, we must use the following operations strictly in the order given below. (a) of (b) division (c) multiplication (d) addition and (e) subtraction.

**Note**: The rule is also known as the rule of ‘VBODMAS’ where V, B, O, D, M, A and S stand for Vinculum, Brackets, Of, Division, Multiplication, Addition and Subtraction respectively.

**Example**:**(1)** What is the total of all the even numbers from 1 to 400?

Solution: From 1 to 400, there are 400 numbers. So, there are 400/2= 200 even numbers.Hence, sum = 200(200+1) = 40200

**(2)** Find all the odd numbers from 20 to 101.

Solution: The required sum = Sum of all the odd numbers from 1 to 101.Sum of all the odd numbers from 1 to 20= Sum of first 51 odd numbers – Sum of first 10 odd numbers=

**Miscellaneous**

1. In a division sum, we have four quantities – Dividend, Divisor, Quotient and Remainder. These are connected by the relation.Dividend = (Divisor × Quotient) + Remainder

2. When the division is exact, the remainder is zero (0). In this case, the above relation becomesDividend = Divisor × Quotient

**Example: 1**: The quotient arising from the divisor of 24446 by a certain number is 79 and the remainder is 35; what is the divisor?

Solution:Divisor × Quotient = Dividend - Remainder79×Divisor = 24446 -35 =24411Divisor = 24411 ÷ 79 = 309.

**Example: 2**: A number when divided by 12 leaves a remainder of 7. What remainder will be obtained by dividing the same number by 7?

Solution: We see that in the above example, the first divisor 12 is not a multiple of the second divisor 7. Now, we take the two numbers 139 and 151, which when divided by 12, leave 7 as the remainder. But when we divide the above two numbers by 7, we get the respective remainder as 6 and 4. Thus, we conclude that the question is wrong.

**Download PDF for Formula Sheets: Number System**

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