Below is a Java applet to compute the check digit for an ISBN for a book. The applet takes the first nine digits from an ISBN as input and computes the tenth (check) digit.

Note:ISBNs are usually printed with dashes between blocks of numbers. It is interesting that the dashes don't always occur in the same locations. The applet below doesn't care about the location of the dashes, or if you leave them out altogether.

## Exercise 1

Find two books of your choosing, and use the ISBN applet to verify that the ISBN from each book has the correct check digit. Give the title, author, and ISBN for each book.

You can use this applet to investigate the following two questions:

## Research Question 1

(a) Does the check digit change if we change one digit of the input?(b) Does the check digit change if we switch two digits of the input?

Section 4.1 | Section 4.2 | Section 4.3 | Section 4.4 | Section 4.5

Copyright © 2001 by W. H. Freeman and Company