After completing this lesson, student must be able to:

- Describe the octal number system.
- Explain decimal and binary number.
- Explain the hexadecimal and binary arithmetic.

The number of base or radix ten is called decimal numbers. It is first number system in which all the ancient and modern mathematical calculation is done. Binary numbers are used to run computer. This note contains description on Decimal and Binary Number system are used to operate computer.

The number with base eight is called octal number. It is represented by Q or 8. This note explains octal number system and its conversions.

The number with base sixteen is called hexadecimal number. We can generate these numbers with the combination of 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A,B, C, D, E, F. Where A=10, B=11, C=13, D=14, E=15, F=16. This note contains description on hexadecimal number system its conversion and binary arithmetic.