Why we are using alphabets(A to F) in hexadecimal systems instead of using numbers after 0 to 9???

Answer 1

The hexadecimal system (base 16) consists of 16 unique digits, whereas our traditional digital (base 10) system has only ten digits (0-9). That's why we have to add six more symbols to represent all digits of the hexadecimal system.

Just like in the decimal system, "10" represents an "overflow" that happens when you ran out of unique digits to use. That's why a hexadecimal "10" is a decimal (1*16^1+0*16^0 =) 16 and a binary (base 2) "10" is a decimal (1*2^1+0*2^0 =) 2. For every system with base > 10 we need to use some non-numerical symbols as our decimal system doesn't have enough numerical symbols.

Answer 2

Because it will be strange,if we have color #AAAAAA,then will be #101010101010

Answer 3

It can't be done. What is 10, is it the number after 9, or an 1 and a 0.