Drop Chance Calculator

Enter a drop rate as a percentage or as a one-in-N chance, say how many attempts you are making, and this returns the chance of at least one drop, the chance of coming away with nothing, and the expected number. Ask for more than one copy and it adds the binomial figures for at least that many and for exactly that many. The second action runs the question backwards: give it a rate and how sure you want to be, and it returns the number of attempts that first reaches it, along with the 50, 75, 90, 95, 99 and 99.9 per cent marks. Every attempt is treated as independent at a fixed rate, which is what a published drop rate means, so pity counters, bad-luck protection and guaranteed drops after N tries will all make these numbers pessimistic.