Board Thread:General Discussion/@comment-5956378-20140429103142/@comment-24577221-20180217201002

The usual probability is pretty close to 1% per try, increased by about 1% for each torch that is lit.

If you're working with no lit torches, it's not surprising that you haven't succeeded yet. 70 tries would give you a 50% chance of getting at least one success.

If you have been working with 10 lit torches, giving a total expected success rate of 11% per try, it is a bit odd that you haven't succeeded. In that case, 6 tries would give you about a 50% chance of at least one success. 31 tries would give you about a 97.3% chance of at least one success. But it still wouldn't be impossible; that means that there would still be a 2.7% chance of not getting anything but the 3-element monsters.