How do you calculate %xHKO?

I'm no good with probability distributions

Basically I'm trying to figure out what damage range I need to
95% 2/3hko each Oblivion monster with Cannon
95% 4/5/6hko each Oblivion monster with Torpedo
95% 3hko Skeles with Torpedo
95% 1hko Skeles with Cannon (if possible o_o) and 2hko with Torpedo

1hko is quite easy to figure, and so is 100% xhko. But I don't know how to calculate points on the bell curve. 100% xhko is overdoing it because it always reports a number way beyond what you actually need.

I'm not really good with the damage formulas, but basically to 1hko a monster with 100 hp at 95% you will need the actual range (after skill modifiers) to be 95-195.

Its like, max dmg - min dmg is your 100%. monster hp - min dmg is the change to 1hko a monster (out of the 100%).
so your chance to 1hko a monster is:
max dmg - monster hp
__________________
max dmg - min dmg


for xhko, i suppose you just divide the monster hp by the number of hits. like, to 95% 2hko the monster above (100 hp) you will need the damage range required to 95% 1hko a monster with 50 hp.