If you are looking for a very special drop, and are wondering about how many mobs it might take, or if you are grinding for an item and didn't get it, you might want to know what the chance of getting it was, and this formula might come in handy. P = % chance to get desired drop. D = drop rate of desired item. (x of x-kills), this means that a 10% drop chance is equal to 0.10. X = the amount of mobs you plan to kill. Expressions in parentheses are to be calculated first.