Question

Compute the 4-bit checksum for the hexadecimal message 5E1D0 and express your result as a hexadecimal digit.

Answer 1

5E1D0 = 0101 1110 0001 1101 0000

To calculate checksum:
first add first 2 digits:
  0101
+ 1110
=10011 
There is 1 as carry, it will again be added to the last 4 bits:
  0011
+    1
= 0100

Now add 3rd hex digit 0001 to it
  0100
+ 0001
= 0101

Now add 4th hex digit 1101 to it
  0101
+ 1101
=10010

Add the carry again to last 4 bits:
  0010
+    1
= 0011

Add 5th hex digit 0000 to it
  0011
+ 0000
= 0011

Now sum is 0011, So checksum is reversed of this, So it will be 1100, which is hex digit C