# Tag Info

5

The mean of 2d20k1 is 13.82 - roughly equal to +3, +4 if rounding up. The median is 15 - equal to +5 The mode is 20... The problem being that, if the TN is greater than 10, the impact is more, while if less than 10, less. For a TN 15+ save, you go from 30% chance to 51% - slightly better than a +4, while on a TN 5+, you go from 80% to 96%, roughly a +3. On ...

13

The answer depends on what you're rolling, what your target number is, and what modifiers are already in place. For D20s, the answer is about five, but less if you need to roll really high or really low. See this answer. In general, the formula for probability of success is: 100% - (chance of failure per roll)^(number of attempts). This applies to Choose ...

4

I can't give you exact probabilities, but I can say that an extra die is strictly superior to a reroll. ("Strictly superior" meaning that it's sometimes better and never worse.) Given this particular set of options, an extra die is nearly always superior. Both are equivalent only when there is no chance of success. In all other cases, an extra die is ...

2

I'm sure it's possible and not too hard to treat your dice rolls as if they were 3d3 and 4d3 giving a success on a roll of 3 (for easier math), calculate the probabilities of getting 1, 2 or 3 successes on the first set and then the probability to get 1, 2, 3 or 4 successes on the second, then seeing which combination of those gives the intended result. I'm ...

3

Rerolls are almost always identical to just adding dice. The only time that rerolls would not be taken as just being additional dice is, to my knowledge, in only two cases: when enough dice succeed to prevent all the rerolls from being used, or when there are too few original dice to make the rerolls practical. If you can reroll failures again, this becomes ...

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