http://www.nytimes.com/imagepages/2009/02/08/arts/20090209_KEN_GRAPHIC.html
Another Japanese puzzle along the lines of Sudoko, except this also requires math.
Named KenKen, how can I resist?
Not bad. Took me a while to get the jist of it…but not bad once you get rolling.
I like it - thanks. David K
I’ve only tried the “hard” 6x6 on the NYTimes site. Having the automated tick system is a boon. I’m hoping the 7x7/8x8/9x9 are harder, as the 6x6 wasn’t too hard. Once you get some filled in and can set up the candidates, it’s like Sudoku solving with the extra hints of the arithmetic.
I struggled with the new 8X8 today. Couldn’t they have started me with an easy 8X8 instead of the tough one? I’ve gotten the 4X4 and 6X6 pretty much down, but adding the 7 and 8 as options really killed me today.
I have had a book of NY Times puzzles for 2 years now. I have never been able to do one without peeking at the answers. It’s such a humbling experience that sometime I feel like an onager. 
I read your post right before I was about to go to bed, so I gave it a shot. Not too bad, but unlike the 4s and 6s, you need to use more “Suduko-style” techniques. Also, I think that the 7s and 5s are a bit of the key, because they’re prime, and also can’t be used in any other number, so if 5 or 7 will go into the * or /, you’ve got one of the numbers. But its a bad idea to do it before going to bed, I couldn’t get arithmetic out of my head all night long.
Pretty cool. The first one was very easy.