5. Why is the check digit often modulo? (Instead of difference or summation?)
2. Is the following valid? C U D = C + D – (C ? D)
Prove using Venn Diagram (make up your own elements to show proof) (around (4 to 5) in each C and D and (2 to 3) in
common) Then show math formula with actual values to prove or disprove.