[RPG] How to calculate dice probability in the A Song of Ice and Fire system


Say I need a net hit of 20 or higher. I get to roll 5d6 base, but I get a bonus dice roll of +3. I only get to keep the 5 highest so I would be rolling "8d6 drop lowest 3 rolls"
I want to know what formula I would use to calculate the probability for these kinds of rolls in the future.

Example explaining the skill system:
[skill] Agility 5, [specialty] Dodge 3. I make a dodge roll, so I roll 5d6 (from the skill) +3d6 bonus dice (from the specialty), but I can only keep 5 dice (because of my skill). So I roll 8d6 total, and drop the three lowest rolls, adding the 5 remaining rolls to see my net roll.

Best Answer

http://anydice.com/ will do this quite easily for you:

Roll 8 drop lowest 3 (which is just keep highest five) :

output [highest 5 of 8d6]

Click "at least" to see the probability of getting 20+, which is 79.97%