(related to Problem: The Mystic Eleven)

Most people know that if the sum of the digits in the odd places of any number is the same as the sum of the digits in the even places, then the number is divisible by $11$ without remainder. Thus in $896743012$ the odd digits, $20468,$ add up $20,$ and the even digits, $1379,$ also add up $20.$ Therefore the number may be divided by $11.$ But few seem to know that if the difference between the sum of the odd and the even digits is $11,$ or a multiple of $11,$ the rule equally applies. This law enables us to find, with a very little trial, that the smallest number containing nine of the ten digits (calling naught a digit) that is divisible by $11$ is $102,347,586,$ and the highest number possible, $987,652,413.$

Thank you to the contributors under CC BY-SA 4.0!



Project Gutenberg

  1. Dudeney, H. E.: "Amusements in Mathematics", The Authors' Club, 1917

This eBook is for the use of anyone anywhere in the United States and most other parts of the world at no cost and with almost no restrictions whatsoever. You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included with this edition or online at If you are not located in the United States, you'll have to check the laws of the country where you are located before using this ebook.