I need help for my contemporarly math final!!?

Question

I have been studying these things all week and simply cannot get it straight in my head how to figure the following:
codabar
code 39
a UPC code
a traveler's check code and
the code for an Avis rental car.
I know that, for instance, with a UPC code, you add the odd digits and multiply that number by 3. You then add the remaining digits and add that total to the first total. You then must add a number that will bring that total to a number that ends in 0. For some reason, I can't get it to work.. and the others are just escaping me.. HELP!!! I need to get this figured out tonight!!

just a quick note.. I am 52 years old.. have been in and out of school a LONG time.. I have read the chapter 6 times. If I understood this stuff, I wouldn't be asking the question.. if I had notes, it would be because I had SOME idea what I was doing.. I need for someone to explain it in PLAIN ENGLISH.. THEN I can use that to work out some practice problems and get it straight in my head..

Answer 1

Try looking in your book again with a fresh eye, after a short break to clear your head.

It should be in your notes and/or book somewhere.

Good luck!