A 12-12-10 difficulty would have 15 mines in it (12 * 12 * 0.10) or 14.4 rounded up.
A 5-10-80 difficulty would have 40 mines (5 * 10 * 0.80) or 40.0 rounded up.
And so on...
Anywhere between 10% and 20% is fun for me...after that it just gets basically unsolvable.
