I am supposed to find if cc numbers are valid based on these rules:
Multiply every other digit by 2, starting with the number’s second-to-last digit, and then add those products' digits together.
Add the sum to the sum of the digits that weren’t multiplied by 2.
If the total’s last digit is 0 (or, put more formally, if the total modulo 10 is congruent to 0), the number is valid!
When I work-it-out by hand, I dont get valid for these numbers... but they are (from the solutions site). Can I see how its done correctly?