- Challenge level = stat - 50/50 chance - flip one coin, must come up heads
- Challenge level is 2 greater than stat - 12.5% chance - flip three coins, all must come up heads
- Challenge level is 2 less than stat - 87.5% chance - flip three coins, one or more must come up heads.
In other words, for challenge levels greater than the corresponding stat, the chance of success is 50% to the power of (the difference between the stat and the challenge level + 1). Flip a number of coins equal to one plus the difference between the stat and the challenge, and all must come up heads.
For challenge levels less than the corresponding stat, the chance of success is 100% - (50% to the power of (the difference between the stat and the challenge level +1)). Flip a number of coins equal to one plus the difference between the stat and the challenge, and one or more need to come up heads.
If you don't want to do the calculations yourself, we have a helpful command in the Discord - simply type '!statcheck' followed by the challenge number, then the skill number (separated by spaces).