Brain Gym

It's great to head down to the gym and get a good workout, but it's also great to do the same for your brain:  to work on a challenging problem or puzzle. A very absorbing logical and arithmetical puzzle is the variation on Sudoku called KenKen:

Here is my detailed solution for the above problem:  

KenKen Puzzle Solution

There is an excellent KenKen web site with many playing tips and tutorials, as well as puzzles at many difficulty levels that can be solved online:  KenKen Official Site

An interview with Tetsuya Miyamoto, math teacher and the creator of KenKen:

From the Official KenKen Site, a brief "How To" video:  

Another excellent introduction by Bill Lombard, this time specifically for the 4x4 KenKen Puzzle:

 Hooked now?  Another problem with a detailed solution:

A detailed step-by-step solving of the above problem:   

KenKen Problem Solution

For the tablet or phone, there is a great and free official KenKen App available:

 KenKen Classic II

Many web sites provide more KenKen type puzzles to solve.  One of the best is the site of that great online Puzzle Master:  Krazy Dad.  He calls his version of these problems "Inkies":

Free Inkies from Krazy Dad

Here is an example: Inky:   Inky 13 from the 4x4 Hard Collection and a detailed solution:

Detailed Solution for Inky 13

For those interested in the history of the KenKen Puzzle there is an excellent Wikipedia page with lots of great information and links:

Wikipedia Page on KenKen Puzzles