The Devil’s Number

Snowdog was in fine form today! He came into the Maths staffroom and let us know that it was Friday 13th. He is full of ….. information. So then Snowdog said:

“Take any four digit number and multiply it by 666. After all 666 is the devil’s number, which is unlucky. Now tell me all the digits in your answer except one, in any order, and I will tell you the other digit”!

The mighty Mathematician then proceeded to complete this trick flawlessly. How did he do it?


About webmaths

I have been teaching Mathematics in Victorian secondary schools for 30 years. I use the www to make my maths lessons better. I hope this blog will give other teachers some ideas to try in their own classes.
This entry was posted in Problem Solving, Show and Tell and tagged , . Bookmark the permalink.

2 Responses to The Devil’s Number

  1. Britt Gow says:

    Thanks for leaving a comment on my blog Jeff! It’s great to find other maths teachers using web2.0 technology in their classes and challenging students to think outside the square. You have a great list of maths blogs that I am going to spend lots of time exploring. Which year levels do you teach Jeff? Perhaps you know of a good maths teacher looking for a job in a rural school? We will be advertising a position at Hawkesdale P12 College soon, after leadership positions are confirmed.

  2. Caroline says:

    666 is divisible by 9 so any multiple of it will be as well. To determine if a number is divisible by 9, you can add the digits of that number together and get a number that is divisible by 9. That means the sum of the digit is in that multiple will be divisible 9 too. So all he had to do was add the digits together and see how much more he had to add to get a number that was divisible by 9.

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