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How do I find two's complement for hex F3A1?

First I converted the number to binary 1111 0011 1010 0001 and then I found two's complement 0000 1100 0101 1111 givin' as result 0C5F which differs from the answer in the book: 0A57

What I'm doing wrong?

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You're not doing anything wrong. Your result is correct. – stevenvh May 18 '12 at 4:40
then the book is wrong, thanks – Jorge Zapata May 18 '12 at 5:16
That book's result is so off that I would suspect it may be the right answer to some other question (a question answer mixup). – Kaz May 18 '12 at 6:18

1 Answer

up vote 3 down vote accepted

Flip 1's to 0's and 0's to 1's (i.e. regular complement). Then add 1.

What you're doing wrong is having too much faith in a book.

But, on the bright side, at least it's some kind of technical book that is probably mostly correct.

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i get the same result, maybe the book has a mistake – Jorge Zapata May 18 '12 at 4:39
1  
yep, just go into Windows 7, bring up the calculator, switch to Programmer under View, select Hex and Word mode, enter F3A1 and then press ±, result is C5F (doesn't display leading 0). – tcrosley May 18 '12 at 5:15
@tcrosley - nonsense, you can do it on sight! :-) – stevenvh May 18 '12 at 5:18
If this was comedians.stackexchange.com you I would vote for you as a moderator :) – MikeJ-UK May 18 '12 at 9:41

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