Octal to Decimal Conversion:
To convert Octal to Decimal, we can use positional notation method.
1. Write down the Octal digits and list the powers of8 from right to left(Positional Notation)
2. For each positional notation of the digit write the equivalent weight.
3. Multiply each digit with its corresponding weight
4. Add all the values
Example

Hexadecimal to Decimal Conversion:
 To convert Hexadecimal to Decimal we can use positional notation-method.
1. Write down the Hexadecimal digits and list the powers of 16 from right to left
(Positional Notation)
2. For each positional notation written for the digit, now write the equivalent weight.
3. Multiply each digit with its corresponding weight
4. Add all the values to get one final value.
Example-
Convert (25F)₁₆ into its equivalent Decimal number.

Steps for Decimal to Binary Conversion.
Step 1: Divide the decimal number which is to be converted by two which is the base of the binary number.
Step 2: The remainder which is obtained from step 1 is the least significant bit of the new binary number.
Step 3: Divide. the quotient which is obtained from the step 2 and the remainder obtained from this is the second least significant bit of the binary number
Step 4: Repeat the process until the quotient becomes zero.
Step 5: The last remainder obtained from the division is the most significant bit of the binary number. Hence, arrange the number from the most significant bit to the least significant bit (i.e., from bottom to top).

(i) ASCII : American Standard Code for Information Interchange (ASCII).
(ii) BCD : Binary Coded Decimal (BCD)
(iii) EBCDIC: Extended Binary Coded Decimal Interchange Code (EBCDIC)
(i) ASCII :   American Standard Code for Information Interchange (ASCII) is a 7-bit code, which means that only 128 (27) characters can be represented. However, manufacturers have added an eighth bit to this coding scheme with which it is possible to represent 256 characters. This 8-bit coding scheme is referred to as an 8-bit American standard code for information interchange. The symbolic representation of letter A using this scheme is 1000001₂(65₁₀).
It is a character encoding standard developed several decades ago to provide a standard way for digital machines to encode characters. The ASCII code provides a mechanism for encoding alphabetic characters, numeric digits, and punctuation marks.
(ii) BCD: Binary Coded Decimal is a 4-bit code used to represent the numeric data alone. For  example, a number like 9 can be represented using Binary Coded Decimal as 10012 . Binary Coded Decimal is mostly used in simple electronic devices like calculators and microwaves. This is because it makes it easier to process and display individual numbers on their Liquid Crystal Display (LCD) screens.
A Standard Binary Coded Decimal, an enhanced format of Binary Coded Decimal, is a 6-bit representation scheme which can represent non-numeric characters. This allows 64 characters to be represented.
(iii) EBCDIC: Extended Binary Coded Decimal Interchange Code (EBCDIC) is an 8-bit character-coding .scheme used primarily on IBM computers. A total of 256 (28) characters can"be coded using this scheme.

A, B, C, D, G, H, I, L, M, N are presents 0,1,2,3,4, 5, 6, 7, 8, 9 respectively of decimal number system  (base 10) so, (INDIAN)_IO = (693609)₁₀
To find its hexadecimal equivalent

Thus (INDIAN)₁₀ = (693609)₁₀ = (A9569)₁₆

645₈
\(\overset { 6 }{ \underset { 110 }{ \downarrow } } \) \(\overset { 4 }{ \underset { 100 }{ \downarrow } } \) \(\overset { 5 }{ \underset { 101 }{ \downarrow } } \)
645₈ = 110100101₂