Board Thread:Game Discussion/@comment-9204520-20130621190525/@comment-10479663-20130621214218

Actually, the 15% is accurate in terms of standard statistics.

You have a 1.612% chance of a success per draw - or a 98.388% chance of failure per draw

A tier 6 purchase guarantees you 10 draws

The probability of getting 10 consecutive failures (no ultra rare) would be:  98.388%^10

That leaves the probability of failing on 10 consecutive draws at: 85.0005%

In turn, the probability of the success condition occurring in 10 draws is 14.9995%... they just rounded.