Saturday, January 3, 2026

2. Number System

2.1 Concept of Number System

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 2.1 Concept of Number System: 

Definition of Number systems, Application of Number system conversion 

 2.2 Binary Calculation: Addition, Subtraction

 2.3 Number Conversion 

 2.3.1 Decimal to Binary, Octal, Hexadecimal. 

 2.3.2 Binary, Octal, Hexadecimal to Decimal 

 2.3.3 Binary to Hexadecimal and vice versa , Binary to octal and vice versa






The concept of numbers developed early in human history when people used fingers, sticks, pebbles, knots of rope, and symbols to count objects and perform simple calculations like addition and subtraction. As human needs increased, different calculating methods and devices were invented. Today, numbers are used in daily life for various purposes such as counting, measuring, and calculating.

 

A number system is a method of writing numbers using a specific set of symbols and rules. Different number systems use different symbols and follow different rules for representing numbers and performing calculations.

 

For example, the decimal number system is the most commonly used number system in daily life. It consists of 10 symbols (0 to 9). Using these symbols, we can represent any number. Due to its simplicity and ease of understanding, the decimal number system is widely used around the world.

 

a) What is a digit? What is a computer word?

A digit is a single symbol used to represent a number in a number system, such as 0–9 in the decimal system.
A computer word is a fixed-sized group of bits that a computer processes as a single unit, usually representing data or instructions.

 

b) Define the base or radix of the number system.

The base or radix of a number system is the total number of unique digits or symbols used in that system.
For example, the decimal number system has base 10, while the binary number system has base 2.

 

c) Which language is used by computer systems, smartphones, and tablets?

Computer systems, smartphones, and tablets use binary language, which consists of only two digits: 0 and 1.

 

Types of Number Systems (Definition with Example)

 

Decimal Number System:
The decimal number system is a number system that uses 10 digits (0–9) and has a base of 10. It is commonly used in daily life.
Example: 456₁₀

 

Binary Number System:
The binary number system is a number system that uses two digits (0 and 1) and has a base of 2. It is used by computers and digital devices.
Example: 1011₂

 

Octal Number System:
The octal number system is a number system that uses 8 digits (0–7) and has a base of 8. It is used as a compact form of binary numbers.
Example: 157₈

Hexadecimal Number System:
The hexadecimal number system is a number system that uses 16 symbols (0–9 and A–F) and has a base of 16. It is widely used in computer programming.
Example: 2F₁₆

 

Application of Number System Conversion

 

Number system conversion has important applications in computer science and digital technology. Since computers use the binary number system to process data, it is necessary to convert numbers between binary, decimal, octal, and hexadecimal systems.

 

In digital logic design, electronic circuits and components work using binary and hexadecimal values, making number system conversion essential. In computer networking, IP addresses are often represented in dotted-decimal or hexadecimal form, so conversion helps in understanding and configuring networks.

 

Number system conversion is also widely used in fields such as cryptography, computer graphics, and signal processing to represent and manage data efficiently. Therefore, understanding number system conversion is crucial for anyone working with digital devices and computer systems.

 

2.2 Binary Calculation

Binary calculation refers to performing arithmetic operations using the binary number system, which consists of only two digits: 0 and 1. Since computers work internally using binary numbers, binary calculations are essential in computer science.

 

There are four main types of binary calculation:

i. Binary Addition
ii. Binary Subtraction
iii. Binary Multiplication
iv. Binary Division

 

Binary Addition

Binary numbers are added in a similar way to decimal numbers, but using only the digits 0 and 1.

Rules of Binary Addition

A

B

A + B

0

0

0

0

1

1

1

0

1

1

1

10 (0 with carry 1)

 

Steps of Binary Addition

Step 1: Align the binary numbers properly, just like decimal addition.
Step 2: Start adding from the rightmost bit.
Step 3: Add the digits using the rules of binary addition.
Step 4: Carry the extra bit if the result is 10.
Step 5: Repeat the process until all columns are added.

Example of Binary Addition

   1100

 + 0101

 --------

  10001

Hence, 1100₂ + 0101₂ = 10001₂

 

Binary Subtraction

Binary subtraction is also similar to decimal subtraction and follows specific rules using borrowing when needed.

 

Rules of Binary Subtraction

 

A

B

A − B

0

0

0

1

0

1

1

1

0

0

1

1 (with borrow)

 

Example of Binary Subtraction

   10111

 - 00101

 --------

   10010

Hence, 10111₂ − 00101₂ = 10010₂

 

Binary Multiplication

Binary multiplication is simpler than decimal multiplication because it involves only 0 and 1.

 

Rules of Binary Multiplication

A

B

A × B

0

0

0

0

1

0

1

0

0

1

1

1

 

Steps of Binary Multiplication

  1. Write the numbers properly aligned.
  2. Multiply each digit of the multiplier with the multiplicand.
  3. Shift left for each next digit (like decimal multiplication).
  4. Add all partial products using binary addition.

 

 

 

 

Example of Binary Multiplication

    101

 ×   11

 -------

    101

 + 1010

 -------

   1111

Hence, 101₂ × 11₂ = 1111₂

 

Binary Division

Binary division is similar to decimal division but is performed using binary digits 0 and 1.

Steps of Binary Division

  1. Compare the divisor with the leftmost bits of the dividend.
  2. If the divisor is smaller or equal, subtract it and write 1 in the quotient.
  3. If smaller, write 0 and bring down the next bit.
  4. Repeat until all bits are processed.

 

Example of Binary Division

1010 ÷ 10 = 101

Hence, 1010₂ ÷ 10₂ = 101₂

 

Exam Practice Numericals (With Carry & Borrow)

A. Binary Addition (With Carry)

   1011

 + 1101

 --------

  11000

Answer: 1011₂ + 1101₂ = 11000₂

 

B. Binary Subtraction (With Borrow)

   10010

 - 00111

 --------

   01011

Answer: 10010₂ − 00111₂ = 01011₂

 

C. Binary Multiplication (Practice)

   110

 ×  10

 ------

  1100

Answer: 110₂ × 10₂ = 1100₂

 

 

D. Binary Division (Practice)

1100 ÷ 11 = 100

Answer: 1100₂ ÷ 11₂ = 100₂

 

2.3 Number Conversion

People commonly use the decimal number system in daily life, whereas computers use binary, octal, and hexadecimal number systems for processing information. Since humans and computers use different number systems, number system conversion is required to convert numbers from one system to another so that both humans and machines can understand them.

There are different methods to convert numbers between number systems.

 

A. Decimal to Binary Conversion

Steps:

  1. Divide the given decimal number by 2 and write the remainder.
  2. Divide the quotient again by 2 and note the remainder.
  3. Repeat the process until the quotient becomes 0.
  4. Write the remainders from bottom to top.

Example:

Convert (13)₁₀ to binary.

2 | 13  → 1

2 |  6  → 0

2 |  3  → 1

2 |  1  → 1

    0

Therefore, (13)₁₀ = (1101)₂

 

B. Decimal to Octal Conversion

Steps:

  1. Divide the decimal number by 8 and write the remainder.
  2. Divide the quotient repeatedly by 8.
  3. Stop when the quotient becomes 0.
  4. Write the remainders from bottom to top.

Example:

Convert (345)₁₀ to octal.

8 | 345 → 1

8 |  43 → 3

8 |   5 → 5

    0

Therefore, (345)₁₀ = (531)₈

 

C. Decimal to Hexadecimal Conversion

Steps:

  1. Divide the decimal number by 16 and write the remainder.
  2. Divide the quotient repeatedly by 16.
  3. Replace remainders above 9 with A–F.
  4. Write the remainders from bottom to top.

Example:

Convert (88)₁₀ to hexadecimal.

16 | 88 → 8

16 |  5 → 5

     0

Therefore, (88)₁₀ = (58)₁₆

 

D. Binary to Decimal Conversion

Steps:

  1. Multiply each binary digit by its place value (powers of 2).
  2. Add all the products.

Example:

Convert (10011)₂ to decimal.



Therefore, (10011)₂ = (19)₁₀

 

E. Octal to Decimal Conversion

Steps:

  1. Multiply each digit by its place value (powers of 8).
  2. Add all the products.

Example:

Convert (157)₈ to decimal.



Therefore, (157)₈ = (111)₁₀

 

F. Hexadecimal to Decimal Conversion

Steps:

  1. Multiply each digit by its place value (powers of 16).
  2. Replace A–F with values 10–15.
  3. Add all the products.

Example:

Convert (1AC)₁₆ to decimal.



Therefore, (1AC)₁₆ = (428)₁₀

 

G. Binary to Hexadecimal Conversion

Steps:

  1. Group binary digits into sets of four from right to left.
  2. Convert each group into its hexadecimal equivalent.
  3. Write the result with base 16.

Example:

Convert (100000110101)₂ to hexadecimal.

1000 0011 0101

 8     3    5

Therefore, (100000110101)₂ = (835)₁₆

 

H. Hexadecimal to Binary Conversion

Steps:

  1. Write the 4-bit binary equivalent of each hexadecimal digit.
  2. Combine all binary groups.

Example:

Convert (9A3)₁₆ to binary.

9 → 1001

A → 1010

3 → 0011

Therefore, (9A3)₁₆ = (100110100011)₂

 

Binary to Octal and Octal to Binary Conversion

Clean steps + clear examples. You can write this exactly as it is.

 

Binary to Octal Conversion

Binary to octal conversion is done by grouping binary digits into sets of three (3) from right to left, because 8 = 2³.

Steps:

  1. Group the binary digits into sets of three from right to left.
  2. If needed, add leading zeros to complete a group.
  3. Convert each group into its octal equivalent.
  4. Write the result with base 8.

Example:

Convert (1101011)₂ to octal.

Binary number:   1 101 011

Add zero →      001 101 011

 

001 = 1

101 = 5

011 = 3

Therefore,



Octal to Binary Conversion

Octal to binary conversion is done by replacing each octal digit with its 3-bit binary equivalent.

Steps:

  1. Write the binary equivalent (3 bits) of each octal digit.
  2. Combine all binary groups.
  3. Write the result with base 2.

 

Example:

Convert (753)₈ to binary.

7 → 111

5 → 101

3 → 011

Therefore,



Quick Reference Table (Exam-friendly)

Octal

Binary

0

000

1

001

2

010

3

011

4

100

5

101

6

110

7

111

 

3. Calculate the following as indicated

a) Perform the following binary addition

i. (11110)₂ + (1001)₂
ii. (1011)₂ + (1001)₂
iii. (101011)₂ + (11011)₂
iv. (1010)₂ + (110)₂
v. (101001)₂ + (1110)₂
vi. (100001)₂ + (100011)₂
vii. (100111)₂ + (11010)₂
viii. (110001)₂ + (100101)₂

 

b) Perform the following binary subtraction

i. (1100)₂ − (1001)₂
ii. (1001)₂ − (110)₂
iii. (11101)₂ − (1010)₂
iv. (101100)₂ − (10011)₂
v. (11111)₂ − (10110)₂
vi. (110011)₂ − (10100)₂
vii. (100100)₂ − (1110)₂
viii. (1000001)₂ − (10101)₂

 

4. Convert the given numbers as indicated

a) Decimal to Binary Conversion

i. (56)₁₀
ii. (78)₁₀
iii. (123)₁₀
iv. (345)₁₀
v. (540)₁₀
vi. (572)₁₀
vii. (546)₁₀
viii. (1098)₁₀
ix. (2103)₁₀
x. (445)₁₀

 

b) Binary to Decimal Conversion

i. (1101)₂
ii. (1010)₂
iii. (10010)₂
iv. (10110)₂
v. (101001)₂
vi. (11100111)₂
vii. (111100)₂
viii. (10010011)₂
ix. (1011100)₂
x. (100110)₂

 

c) Decimal to Octal Conversion

i. (69)₁₀
ii. (216)₁₀
iii. (767)₁₀
iv. (79)₁₀
v. (443)₁₀
vi. (413)₁₀
vii. (765)₁₀
viii. (1334)₁₀
ix. (1825)₁₀
x. (2783)₁₀

 

d) Octal to Decimal Conversion

i. (124)₈
ii. (242)₈
iii. (333)₈
iv. (763)₈
v. (103)₈
vi. (451)₈
vii. (3401)₈
viii. (1045)₈
ix. (438)₈
x. (611)₈

 

e) Decimal to Hexadecimal Conversion

i. (55)₁₀
ii. (540)₁₀
iii. (225)₁₀
iv. (880)₁₀
v. (2046)₁₀
vi. (2024)₁₀
vii. (6678)₁₀

 

f) Hexadecimal to Decimal Conversion

i. (56)₁₆
ii. (67)₁₆
iii. (558)₁₆
iv. (B74)₁₆
v. (20D3)₁₆
vi. (DEF)₁₆
vii. (6E3)₁₆
viii. (63F)₁₆

 

g) Binary to Hexadecimal Conversion

i. (1000110)₂
ii. (11001)₂
iii. (1111000)₂
iv. (11110000111)₂
v. (101010110)₂
vi. (1110010110)₂
vii. (11011001)₂
viii. (1001100)₂

 

h) Hexadecimal to Binary Conversion

i. (D4)₁₆
ii. (643)₁₆
iii. (189)₁₆
iv. (2BF)₁₆
v. (A9F)₁₆
vi. (FACE)₁₆
vii. (FB4)₁₆
viii. (1B2)₁₆

 


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