How to Verify an ISBN

ISBN is abbreviation of International Standard Book Number, which usually can be found on the back of a book. 

This instructable is designed to help people find out whether a ISBN is valid using easy mathematics.

You will only need a pen/pencil, a piece of paper. 

Find out what kind of ISBN you have.

Two kinds of ISBN is now used for a book, 10 or 13 digits.

Usually, a 13 digits ISBN is converted from a 10 digits one by adding a "978" prefix and alter the last digit, which is often called the check digit.

Step 2-4 for 10 digits ISBN.
Step 5-7 for 13 digits ISBN.

In case you have a 10 digits ISBN, for example, the ISBN for the book Gravitation . 
0-7167-0344-0
You need to assign the position of each number from left to right.

Multiply each number by its position number and then sum up the products.

Divide the sum by 11 and find out what is the remainder. 
If the remainder is zero, then it is a valid 10 digit ISBN.
If the remainder is not zero, then it is not a valid 10 digit ISBN.

If you have a 13 digits ISBN. 
978-0-7167-0344-0
Also assign the position of each number from right to left

Multiply each number by an alternating 1 and 3 and then sum up the products.
Odd number positions by 1.
Even number positions by 3.

Divide the sum by 10 and find out what is the remainder.
If the remainder is zero, then it is a valid 13 digit ISBN.
If the remainder is not zero, then it is not a valid 13 digit ISBN.