Friday Puzzler -- Chocolate Bar
Alex Y
A chocolate bar is scored to allow it to be broken into smaller rectangles. The scoring is such that the "grid" of chocolate rectangles is m pieces in one direction and n pieces in the other.
If you break the bar using only straight-line breaks in the original bar and in the resulting pieces until the bar is broken into all the individual rectangles, how many breaks must you make? Each break is of a single piece of chocolate--no stacking the pieces and breaking multiple pieces at once.
Extra credit for the "aha" solution to this one -- I got it only by brute force, but maybe even if you do that, you can look for the "aha".