In writing the answer to problem 1, I failed to see the minus sign on the
second number, -17.
17 is 0001 0001, so -17 is represented by its 2's complement:
1110 1110
+1
---------
1110 1111
Thus I should have added:
1100 1001
1110 1111
---------
1011 1000
There is a carry into the sign bit and a carry out, so there is no
overflow. The answer is negative. We do the 2's complement to find the
absolute value:
0100 0111
+1
---------
0100 1000 which is 72
Thus the answer to the problem is -72.