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 second this question. I didn't pass my Statistics class, so this is a mystery to me. To make matters worse, crits completely throw the whole thing for a loop. Is anyone here a Math PHD?