+50 Let's play mini-Sudoku!
We wish to place an "X" in four cells, such that there is exactly one "X" in each row, column, and 2x2 outlined box.
For example:
In how many ways can we do this?
(Terminology: A cell is one of small 1x1 spaces. A box is one of four outlined 2x2 group of cells.)
+129899
This was answered a while back, but the answer ends up being 16
4 ways to place the X in the top row
2 ways to place the X in the second row [ in the other 2 x 2 box not occupied by the first X ]
2 ways to place the X in the third row [ we can choose either of the two empty columns]
Only 1 way to place the last X in the last empty column
So ....4 x 2 x 2 x 1 = 16
+9481 Here's the older one if it helps any: https://web2.0calc.com/questions/question-asap 
