What must be and what can't be

Have you heard of KenKen puzzles? They are logic puzzles like Sudoku but with an extra element of math calculation. They are great challengers for people of all ages and abilities, since there is such a great range of levels of difficulty. I’ve given them to students, teachers, and friends. 


My dad first introduced them to me. He must have discovered them when they showed up in the New York Times on the same page as the crossword puzzle. He does them in pen, with many cross-outs. The answers to the previous day's puzzles are always there, but they are unnecessary. You know when you've got it right.

I have figured out how to do KenKen puzzles and can do an OK job, especially with the easier puzzles. I want to be better than I am now, so I know I need practice. My dad and mom are visiting me in Vermont this week, so I decided to see if I could get some help with my KenKen chops.

Here is my dad’s advice to me: “First you look at the arithmetic, put in some candidate numbers. Then you start looking for what must to be and what can’t be. Remember to see the whole puzzle even as you work on the pieces. Don’t quit. Keep looking for what must be and what can’t be. If you look at it a little bit you will see it. If you get really stuck, go pour yourself a glass of Pinot Noir or something and the answers will become evident.”

Dad is all about creative problem-solving perseverance, which means he is down with the Math Common Core without knowing it. I was stuck on the harder of the two New York Times puzzles today but he freed me with one little tip. I filled in the rest of the numbers almost as fast as I could write. The tip went something like, “This has to be a 5 and that can’t be a 5 so it must be a...”.

KenKen puzzles are great for young mathematicians. My youngest KenKen student was in first grade. I think most first graders are too young, but she nailed it. I like giving out packets that start with the easier 3x3 grids and are limited to addition and subtraction, and then progress to larger grids with multiplication and division. Most students can quickly find a just-right puzzle and dive in.

The best part of this story is that the marvelous Phia S., a student entering fifth grade, loves KenKens so much she decided to write her own. Here is a photo of the treasured book of KenKen’s given to me by Phia. 

Phia's amazing KenKen book

So, enjoy your summer and take your KenKens (and Pinot if you are of age) to the lake or wherever you might be relaxing. The New York Times publishes two a day on the crossword page (they always include the directions) and more online. Cheers!