Single post in Contests

There are 60 combinations. Obviously the first one is unique (100%) For the second to be unique, there are 59/60 options. 98.33% Third one has to avoid two combos. 96.67% = 95.06% total Fourth: 95% = 90.3% total Fifth: 93.33% = 84.28% total As you can see, that's 15.72% chance of having a duplicate within 5 Contests. Not surprising at all.