I hate the fact that Cisco wont let you bring in a calculator to convert between number systems - how many people can do that quickly? I can, but just not fast - even for simple numbers.
To convert a hex number to decimal is easy.
0 - 9 in hex = 0 - 9 decimal
A - F in hex = 10 to 15 in decimal
Each place equals 16-to-the-power-of the place (remember that we start at the right and go left, and the first place is power-0 not power-1). So if you have the hex string "A" then you know it is 10 * 16^0 or 10. If it was "1B" then you know that it is 1 * 16^1 + B(or 11) * 16^0, the total is 16 + 11 = 27.
Now, how about converting decimal to binary?
Easy.
Same technique, however we are at base-2 not base-16, so instead of 16^1 we use 2^1.
The number 10(dec) in binary is 1010.
Why?
This is not the number 1,010, it is actaully 1 * 2^3 + 0 * 2^2 + 1 * 2^1 + 0 * 2^0. Do the math:
1 * 2^3 = 8, and 1 * 2^1 = 2, add together, 8+2, and the total is the answer - 10. Forget about anything that is "0" in binary, because we would do this 8 + 0 + 2 + 0, the end result is the same, so it makes it shorter to write out.
