Get 5 NV stacks before killing a KeyWarden
MP Level determines drop rate : MP1 = 10% ... MP5 = 50% .... MP10 = 100%
I have done several runs in a row on the A3 Warden. my results were 0 keys.
7 Runs were done : Mp4, Mp4, Mp4, Mp4, Mp4, Mp4, Mp4.. and no keys.
The formula to calculate your drop chance ( x ) over any given number of runs ( y ) is this:
1 - ( ( 1 - x ) ^ y )
Using the nifty calculator at http://wow.joystiq.com/2010/01/13/drop-chance-probability/ that according to probability that there should have been a 97.20064 percent chance of the item dropping in the given number of runs.
Has the key drop rate been reduced from 10% per MpLvl ?
edit : +2 runs, still no key. up to 98.99223 of the item having supposed to drop
Further calculations for other MP Levels, assuming the 10% chance per MpLvl is right
Mp1 x 7 runs = 52.17031 %
Mp2 x 7 runs = 79.02848 %
Mp3 x 7 runs = 91.76457 %
Mp4 x 7 runs = 97.20064 %
Mp5 x 7 runs = 99.21875 %
Mp6 x 7 runs = 99.83616 %
Mp7 x 7 runs = 99.97813 %
Mp8 x 7 runs = 99.99872 %
Mp9 x 7 runs = 99.99999 %
Mp10 x 7 runs = 100% every run