Alexander Garden, on 17 September 2015 - 03:04 PM, said:
All maps have equal weighting during this event, which should help.
A little, but I mean, if you've ever tried collecting cards or something you know how bad it can get when you near the end. Bear with me, because once you get halfway through you start to see how many attempts it will really take.
For the first half, it's pretty straightforward to calculate your probability. To get any of the 9 solo/group queue maps, you have a 100% chance to succeed in one attempt.
Then you need any of the 8 remaining. You will probably get it -- 89% chance. Then 78%, 67%, 56%.
Now you need any of 4 remaining maps. You will probably not get it the first time, but there is a 75% chance that you will succeed within two attempts.
For the remaining 3, there is a 56% chance you succeed within two attempts.
With 2, there is a 53% chance within three attempts.
For your last map, there is a 51% chance of getting it within six attempts.
TLDR: If you are neither lucky nor unlucky, it will take 18 matches to get all nine maps at least once. If you fail to get the required score for a map, you will need to play six more matches to be likely to get it again.