I have good news for owners of the iPhone and/or the iPod Touch. I've just doubled the size of the iPhone/iPod Touch Mental Gym!

In addition to the four challenges that were already there, four new brain-bending games have been added:

* 15 Puzzle: While there have been several versions of the 15 puzzle made for the iPhone, this is the first one I've found that both employs the classic numbered squares, and will properly scramble the puzzle for you. This makes it the perfect tool, not only for learning to solve this classic puzzle, but also for learning how to arrange a magic square on it, as in my video.

* Calc10: This is one of those games that's so simple, it proves surprisingly addictive. In this game, you're given four random numbers from 0-9, the four basic arithmetic operators (addition, subtraction, multiplication and division) and a memory function. Using each of the four numbers only once, and finishing with the memory function empty, you must figure out how to arrive at a total of 10 as quickly as you can. Sometimes, this is very easy, such as when you get the numbers 0, 8, 7 and 2. Here, you would simply hit 7 * 0, giving 0, then add 8 and add 2, resulting in 10. It can be get much harder, though, like the time I got the numbers 9, 6, 6 and 9. Can you make 10 out of that (remember, you must use all four numbers)? There's a reset function, which clears the calcuator and gives you back all your numbers, but doesn't reset the clock. Finally, the solution function can be used when you can't solve the puzzle. This is also very helpful in teaching you approaches you may not have previously considered.

* Lights Off: As you might guess from the name, this is a version of the puzzle best known as Lights Out. Any time you press a lighted button, it will turn off, and pressing a dark button will light it. The object is to turn off all the lights on the board, which would be simple if it weren't for the fact that touching any button will not only flip its own state, but that of the buttons directly above it, below it, to its right and to its left. Ideally, you want to shut all the lights off in under 15 moves. You can learn to do this in two steps, first by learning how to solve the puzzle, then by learning how to solve it in the minimum number of moves.

* Peggy: This is the classic Peg Solitaire game, played on the classic English board. The only way to move a peg is by jumping over another peg that it directly above it, below it, to its right or to its left into an empty space. When a peg is jumped, that peg is removed from the board. The challenge is to finish with only one peg left on the board, ideally in the same space that was initially left empty. While Wikipedia lists many great peg solitaire links, I would particularly like to draw your attention to George Bell's Peg Solitaire Page, for those who want to understand more about the game itself.

Please take some time to play and enjoy these games, and let me know if you other suggestions for the iPhone/iPod Touch Mental Gym.

Oh, and for those of you wondering about my 9, 6, 6, 9 challenge from the Calc10 section, here's the solution. First, you would click on 6, then divide it by 9, giving an answer of 2/3. This is stored in the memory function. Next, you add 6 + 9, which is 15. Now, you hit the multiplication button and memory. This is 15 times 2/3, which is 10!