Mathematically Yours

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Publishing a book of short stories also involves doing some mathematics. How?

Look, I've got an ISBN number from the authorities for the book. When I receieved it, it read some thing like this:

ISBN 81-7525-729-X.

I thought "X" is something open to the author to put to identify his/her book, say 1 or 2, or 3.... This means, as I understood, I had the choice of using the number 10 times (from 0 to 9) in place of "X" and can go ahead with the plan of publishing ten books. Yes, beyond 9 I knew I would not be able to use it. And I knew an ISBN number cannot exceed 10-digit limit.

But what I missed was that "X" represents a check digit. This I got clarified reading an article in Wiki.

Its calculation is a bit typical, if not complicated. Say, I had to multiply the position number of each digit from left onwards, add such products and then divide the sum by 11. Then depending on the remainder, I had to determine the extent to which the remainder fell short of 11. That's all. I've reached my check digit.

Easy, isn't it?

Ok, ok, I'll give the exact calculation. It's as follows:

10 x 8 + 9 x 1 + 8 x 7 + 7 x 5 + 6 x 2 + 5 x 5 + 4 x 7 + 3 x 2 + 2 x 9 = 80 + 9 + 56 + 35 + 12 + 25 + 28 + 6 + 18 = 269

269 / 11 = 24 and remainder 5

11 - 5 = 6

So, my check digit is 6.

And my book will bear an ISBN number like this: ISBN 81-7525-729-6.
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By
A. N. Nanda
11/02/2007
Bhubaneswar.
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