If you are trying to calculate the probability that atleast one of several chance events will occur you must calculate the probability that NONE of those events succeed and your answer will be 1 minus that value. For instance, a character has 5 ToTF relics and you want to calculate his chance to revive with those relics. Knowing that the first ToTF relic has a 0.5 (same as 50%) chance of succeeding thus a 0.5 chance of failing and all successive ToTF relics have a 0.1 (same as 10%) chance of succeeding thus a 0.9 chance of failing, we can infer that the probability of them all failing is 0.5 * 0.9 * 0.9 * 0.9 * 0.9 = 0.32805 (same as 32.805%). Thus the chance of one or more of those relics successfully firing is 1 - 0.32805 = 0.67195 (same as 67.195%). This method can be used with any number of events.