why 6 is added in BCD addition when the result is greater then 9?  *Your answer

In Binary Coded Decimal (BCD), each digit of a decimal number is represented by a four-bit binary number. The decimal numbers 0-9 are represented by their respective 4-bit binary equivalents in BCD.

However, the 4-bit binary numbers also include representations for decimal numbers 10-15 (A-F in hexadecimal), which are not used in BCD.

When adding two BCD numbers, if the sum is 10 or more, it will be represented by one of these unused 4-bit binary numbers. To correct this, 6 (0110 in binary) is added to the sum. This increases the value to a two-digit BCD number, where the second digit is the correct representation for the sum.

For example, if you add 8 (1000 in BCD) and 2 (0010 in BCD), the sum is 10 (1010 in binary). Adding 6 (0110 in binary) gives 16 (10000 in binary), or 10 in BCD (0001 0000), which is the correct representation for the decimal number 10.

So, 6 is added in BCD addition when the result is greater than 9 to correct the sum to a valid BCD representation.