Quote Originally Posted by 'BobGnarly',index.php?page=Thread&postID=93894#pos t93894
If the item has a 15% chance to drop, then the chance for it not to drop in one run is 85% (or 0.85 for math purposes).

The chance for it not to drop in 2 runs is 0.85*0.85.

The chance for it not to drop in N runs is 0.85^N.

I'm not sure how you're coming up with numbers when he didn't say how many runs he did, but let's say it's 25:

0.85^25 = 0.017197... ~= 1.72% chance of happening.
Yeah, like I wrote in a previous post:
Quote Originally Posted by 'Fuzzyboy',index.php?page=Thread&postID=93862#post 93862
Btw, assuming drop chance if 15%, the chance of not getting one in 25 runs is like 1.7%
The 0.75 pct from the second post was was a miscalculation (i typed wrong on the calc i guess) - if the drop chance is 20%, the chance of not getting one is in the area of 0.4 % (however the chance is 0.075% if the dropchance is 25% - perhaps that's what caused it).

The number 25 I just grabbed from thin air (one guy mentioned 23 runs. The original poster didn't mention a number, but I'm assuming it's more than 25 since I took 32 runs and still wasn't exalted in spite of having done a good deal of sha'tar quests before the runs. The exact number isn't really important - I was simply trying to establish that while the chance of not getting one in x amount of runs (25 being the random choice) was very small it was still an possibility.