As there are so many rare items in MMO games, and the probability of getting them varies, but is generally 1% I started wondering how many kills are needed to get an almost certain chance of getting an item.
With a 1% drop rate it might seem on the surface (when I disengage my brain) that killing the creature 100 items will get you the item. Not so, and the math is somewhat tricksy.
WowWiki: An item has a 1% droprate from a specific mob, which means that, on average, one will drop for every 100 kills. This does not mean that it’s guaranteed to drop by the time you’ve killed 100 mobs — it’s an average.
Thankfully somebody has already created a tool which does just that – mobs2kill. What I like about this little webtool is that you can input the drop rate, and what certainty you wish to achieve, and mobs2kill will tell you approx how many attempts are needed. So when considering that some Legendary items require 2 items to drop, each with a 1% drop rate, it makes sense why these things are exceedingly rare.
So to have an almost certain (99%) chance of a 1% drop item that you are farming, you need to kill the mob 459 (ahem 458.21) times. Wow. That said, if you’re happier with 50% overall chance, then you’re only up for 69 kills. For that one item.
And the probability of having the item after 100 kills for a 1% drop rate is a touch higher than 63%. Unsurprisingly the overall odds of having the item get better with each attempt, despite the individual instances of the chance staying at 1%. Farm. Farm. Farm.
- Whine about Bindings of the Windseeker (typhoonandrew.wordpress.com)