User blog comment:ReddUT/How to calculate probability of obtaining something you want from Top 50 decoders./@comment-34159228-20171215043629

0.01 (chance to obtain best item) x 0.02 (chance to obtain one desired best item among best item if there are 50 in total) = 0.0002

[0.02% percent of obtaining desired best item among best item with the assumption that all best items share the same probability to be obtained and 99.98% of not obtaining best item]

If there is x8 event for one specific item but not for the rest

0.01(chance to obtain best item) x 0.16 (chance to the  best item that is x8 in probability in obtaining it among best item if there are 50 in total) = 0.0016

 [0.16% percent of obtaining desired best item among best item with the assumption that all best items share the same probability to be obtained and 99.84% of not obtaining best item]