[Ihavenoname248]

It's the same idea as rolling two dice and having the result be the same. In this case, it's rolling 10 d290s or something, seven times.

Because I'm curious, approximate odds of a duplicate song... 85.48% per division that there won't be a dupe in any one division, 33.34% that there won't be a dupe in any division. That means that there's actually roughly a two thirds shot of a duplicate song showing up, assuming all division song pools are equally sized. If they aren't, the odds of a duplicate only grow larger.