Question

1:
Add 247 and 456 using BCD Addition
and Subtract 147 from 206 using BCD
Subtraction​

Answer 1

Explanation:

In binary subtraction, we find the 2's complement of operand b by inverting all bits and adding a 1. When adding this to a you have performed a−b. In BCD we have to find the 10's complement. This is done by subtracting 9 from each decimal digit (a 4 bit binary number) and adding a 1. Now, using ordinary BCD addition rules we add the two numbers.

Example:

10's complement of 0101 0110 is 0100 0100 (subtracted 9 from each 4 bit segment and added a 1 to the last one. Notice that this could overflow when finding the 10's complement of 0000. You would have to correct the BCD number.).

Now adding 1001 0011 and 0100 0100:

10010011+01000100=11010111

Correction is done when a digit acceeds the value 9 (1001 in BCD). The first digit is correct. The second digit is invalid. To correct it we add 6 (0110 in BCD). 1101+0110=0011 (ignore overflow).

So:

11010111 becomes 00110111

Therefore:

10010011−01010110=00110111

Let's check if this is correct:

10010011=93

01010110=56

93−56=37=00110111