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Week 9 Lecture Notes

Week 9 Lecture Notes - March 3 Lecture 25 Announcements...

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March 3: Lecture 25 Announcements Assignment 5 due (3/11) at 11:55 Last day to sign up for extra credit experiments is 3/12 Error-Detecting Codes Binary Checksum Credit Cards/Luhn Algorithm UPC ISBN: book numbers ISBN : Ex : 1-57586-216-? Method 1 of validating its code 1. Moving right to left : multiply each number by its place in the sequence, starting from 1 2. Sum the results 3. Check that sum(mod 11) = 0 Thus, in 1-57586-216-? (?x1)+(6x2)+(1x3)+(2x4)+(6x5)+(8x6)+(5x7)+(7x8)+(5x9) +(1x10) = 247 + ? Sum = 247 + ? convert to nearest factor of 11, thus 253 Thus, ? = 6 because 247+6 (mod 11) = 0 Method 2 of validating its code 1. Moving left to right : multiply each number by its place in the sequence, starting from 1 BUT NOT including the check digit, which is the last digit on the right side 2. Sum the results 3. Compute sum(mod 11) = N; N = check digit
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Thus, in 1-57586-216-? (1x1)+(5x2)+(7x3)+(5x4)+(8x5)+(6x6)+(2x7)+(1x8)+(6x9 Sum = 204 N = 204(mod 11) = 6 Thus, the check digit is 6 Finding the wrong digit : Ex : 0-385-495 5 2-3 (Second 5 is wrong; find right number) Using method 2 ,
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