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# Calculate Check digits using Modulus 11

This question requires using the check-digit formula presented in this chapter.

(a) Calculate check digits for teh following hypothetical account numbers: 4388, 5100, and 9106.

(b) Verify the following codes (which include a check digit): 10307, 50008, and 22222.

SEE ATTACHED EXPLANATION OF CHECK DIGIT.

#### Solution Preview

You have two key elements in obtaining your single, check digit:

1] A key string of numbers, in your case 5432
2] A proper number to use to find the modulus of the product. This is just a way to say the result when given a number we subtract it from the next highest multiple of something, in your case 11. (As you learn more mathematics, you will see this is not the only way to define "modulus"

Now, we take any four-digit string and take the first digit time the first in our key (here five) and sum that product in order through to the fourth number that we want to get a check digit for times the fourth digit in the key (here, two).

Here are your encodings for (a) - Check all this work, to better understand it!

So, for 4388: 4*5 + 3*4 + 8*3 + 8*2 = 30 + 12 + 24 + 16 = ...

#### Solution Summary

Step-by-step instructions on calculating and verifying check digits using Modulus 11 including a special case.

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