The history and rules of this game can be found at http://en.wikipedia.org/wiki/24_Game.

This app can be used several ways:

As a puzzle solver, you can select the numbers from the drop-downs and then press either of the “Solution” buttons to see solution(s) in the area below the calculator. There may not be any solutions or there may be many.

As a game, you can press either of the “Random” buttons to get a game. These are guaranteed to have at least one solution. When you have a solution you can check it using “Calculator” or the “Solution (all)” button.

As a trainer, use “Calculator” and “Solution” to explore number operations and the various techniques of solving the puzzles.

“Calculator” allows you to try things and check your solution. The “C” button resets the calculator to start over while the “CE” button operates as more of an UNDO stack. After you hit the equals sign, you may use either “CE” or “C” to continue.

Support is at https://groups.google.com/d/forum/xxiv-game-and-solver.