Originally Posted by bbomber72000
This is the odds he'll get it before he runs out of sirens. Not the odds of it being dropped.
First off when applying probabilities for indepedant events, you multiply the odds, not add them. Since each Pink Tail has a chance to drop it, and is in no way affected by it's fellow Pink Tail's, then you have to consider the absolute bare minimum for it to occur. In this case, the chance for one Pink Tail to drop is 1/64 * 63/64 * 63/64 * 63/64 * 63/64. These are the chances that a single Pink Tail will drop from one monster (1/64), and not drop/something else drop from the others (63/64). This comes up with 0.0146710882... whatever, which equated to around 1.4% chance to drop. Anything beyond that (two tails dropping, three tails dropping etc.) could be added on this, but the numbers become so astronomically small that they're not even worth mentioning. The chances of five dropping in one battle are 1/1073741824. Back on topic, fighting with 20 sirens, you have a 28% chance on average for at least one pink tail to drop. Mathematically speaking you need to fight at least 72 battles to guarantee one to drop. However as I have previously mentioned this is all irrelevant in the face of FF4's "unrandom-random" number scheme.