MathDoku

MathDoku now featuring a Holo-inspired design and more user-friendly functionalities.
Also known as Mathdoku, this KenKen game will test your mental arithmetic and challenge your mind. The goal is to fill in the entire grid with numbers while meeting the operation restrictions for each grid cage.

KenKen and KenDoku are trademarked names for a style of arithmetic and logic puzzle invented in 2004 by Japanese math teacher Tetsuya Miyamoto, who intended the puzzles to be an instruction-free method of training the brain. The names Calcudoku and Mathdoku are sometimes used by those who don't have the rights to use the KenKen or KenDoku trademarks.

The objective is to fill the grid in with the digits 1 through 6 such that:

Each row contains exactly one of each digit
Each column contains exactly one of each digit
Each bold-outlined group of cells is a cage containing digits which achieve the specified result using the specified mathematical operation: addition (+), subtraction (−), multiplication (×), and division (÷). (Unlike Killer Sudoku, digits may repeat within a cage.)

Some of the techniques from Sudoku and Killer Sudoku can be used here, but much of the process involves the listing of all the possible options and eliminating the options one by one as other information requires.

In the example here:

* "11+" in the leftmost column can only be "5,6"
* "2÷" in the top row must be one of "1,2", "2,4" or "3,6"
* "20×" in the top row must be "4,5".
* "6×" in the top right must be "1,1,2,3". Therefore, the two "1"s must be in separate columns, thus row 1 column 5 is a "1".
* "30x" in the fourth row down must contain "5,6"
* "240×" on the left side is one of "6,5,4,2" or "3,5,4,4". Either way the five must be in the upper right cell because we have "5,6" already in column 1, and "5,6" in row 4. Also, then the combination must be "3,5,4,4" because there is nowhere to put the 6, with the above criteria.
* etc.
More : https://en.wikipedia.org/wiki/KenKen