Computer Science for IGCSE & O level - Data Transmission (Section 15 - No. 11)
In the ISBN-13 example, what calculation is made with the digits of the ISBN to calculate the check digit?
Multiply each digit by 2 then add them up.
Multiply alternate digits by 3 and add them up with the others.
Add all digits.
Divide by 10.
Explication
Multiply the alternate digits by 3.