It's been more than 10 years since I was in high school, and I'm struggling to make a formula for a game I'm making.

I have a 2 variables, playerSkill and minimumSkillNeeded.

playerSkill can be 0.0 - 100.0

minimumSkillNeeded can be 0.0 - 100.0

When the player tries to do an action, I need to take the playerSkill and the minimumSkillNeeded, and the higher the playerSkill, the more likely it will succeed. Maybe I take the playerSkill, subtract the minimumSkillNeeded, and use the difference as the modifier, while if it's a negative number it returns no chance of success.

Right now I'm just rolling a random number 1-5, if 3 or below it succeeds, which is 3/5 odds.

Another question is how to represent an arc in an equation? Like for skill gain in a game where you start at 0.0, and as you succeed in performing an action it increases based on the difficulty of the action. Right now it just awards the same amount of skill for any success no matter how difficult the task was.

a = formula where a starts at 0.0 and can rise to 100.0

Thanks for any pointers