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Signed binary multiplication 
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#1
Apr108, 11:20 AM

P: 186

15X7
3. The attempt at a solution  I can't seem to figure this one out for some reason. My first attempt, I used 1111(15)X1001(2's complement of 7), but I can't get the right answer. I believe that the answer should come out to be the 2's complement of 105 since the actual answer is 105, but I can't get that. Please help. 


#2
Apr108, 11:26 PM

P: 5

Your problem is due to the way in which you have defined your numbers. When using signed numbers the MSB is actually 8.
So, 1111 = 8+(7) = 1 and 1001 = 8+(1) = 7. To get the correct answer you need to add another MSB such that the MSB now equals 16. Then, 01111 = 15 and 11001 = 16 +(9) = 7. To do the multiplication; 01111 X 11001 = 15X(16) + 15X9 = 105. 


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