# Hexa to Decimal Conversion, Binary to Decimal Conversion?

1. Apr 7, 2009

### kloong

1. The problem statement, all variables and given/known data
1) How to convert 101010.0101B to decimal?

2) and Hexa number 17DB.C to Binary.

3) and lastly, -101 (decimal) to the 2's complement form.

2. Relevant equations

3. The attempt at a solution
for the first one, clearly my problem lies at .0101B. I thought it's 1X10^-2 + 1X10^-4. Is it correct?

for the second one, im not sure what the answer is because of the ".C"

third, i know how to do 2's complement for those without negative. So how should i do those with negative sign?

2. Apr 7, 2009

### mgb_phys

There isn't really a standard for decimals in binary - you normally use IEEE floating point format.
But I would interpret the digits after the decimal point to be 1/2, 1/4, 1/8 etc as you have done.
Again for 2, I would say the decimal is 0xC/0x10 = 12/16=0.75

This is a good explanation of twos complement http://en.wikipedia.org/wiki/Two's_complement

3. Apr 7, 2009

### DoctorBinary

You're on the right track, but use powers of two instead: 1X2^-2 + 1X2^-4.

You can check your answer with a decimal/binary converter (one that converts fractional values as well as integers), such as the one I've written: http://www.exploringbinary.com/binary-converter/

Do you know how to convert the 17DB part? There's a shortcut, and it involves writing out the binary equivalent of each hexadecimal digit. Once you know that, the .C part is similar.