Practice 4: Check Digits for Credit Cards

Mathematics 488 (Digital Codes)

Joseph Malkevitch
Mathematics and Computing Department
York College (CUNY)
Jamaica, New York 11451-0001


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These questions do not involve actual credit card companies.

1. Determine if the following are "legal" credit card numbers by seeing if the check digit is consistent with the other digits:

a. 7799-1234-5465-1110

b. 7799-1234-5465-1112

c. 7799-4321-5465-1112

d. 7799-4323-5465-1112

2. Determine the check digit (?) for the "fake" credit card numbers below:

a. 7799-1234-5678-910 (?)

b. 7799-4321-5678-910 (?)

c. 4444-2212-3313-444 (?)

d. 5555-6666-7777-888 (?)