Check digits
The multiply, add, divide-by-10 method with a worked example and a practice question.
Transcript
A check digit is the final digit of a code. It is calculated from all the other digits.
It is used on barcodes, book numbers, vehicle identification numbers, and credit cards.
The method: multiply each digit by its position, add the totals, and divide by ten. The remainder is the check digit.
Take the code nine four five three four four. Multiply and add: nine, eight, fifteen, twelve, twenty. The total is sixty four.
Sixty four divided by ten leaves a remainder of four. That matches the last digit, so the code is accepted.
Now try three five two one three two. Multiply and add: three, ten, six, four, fifteen. The total is thirty eight, and the remainder is eight.
The last digit is two, not eight, so the code is rejected.
Multiply by position, add, divide by ten. Compare the remainder with the check digit.
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