Colmarr
First Post
Close. It's the number of dice, not the type of dice, that affects your chance of getting the average.
For example, if you roll a d20, you have an equal chance of rolling each possible result between 1 and 20. Each has a 1 in 20 (or 5%) chance.
Now take the attached picture. It is a table showing all the possible combinations of rolling 2d10. The blue column on the left is the first die (and its results from 1 to 10). The red row at the bottom is the 2nd die (and it's results of 1 to 10). The white squares in the middle show the totals of each dice combination.
Eg. cross reference Red 3 and Blue 6 and you'll see the total is 9.
Now if you look at the totals, you'll see that there are 100 possible combinations (the white area is 10 squares by 10 squares = 100).
Of those possible combinations, only 1 gives a total of 2 (the bottom left square, which is the total of Red 1 and Blue 1). Therefore your chance of rolling 2 on 2d10 is 1 in 100 (1%). That's a significantly lower probability than if you were rolling 1d20 (5%).
Conversely, there are 10 ways you can get a total of 10 (Blue 1 Red 9, Blue 2 Red 8, Blue 3 Red 7 etc), which is a 10 in 100 chance or 10%. That's a significantly higher probability than if you were rolling 1d20 (5%).
Adding more dice gives you more possible combinations, and because more of those combinations will add up to middle values (like 9, 10 and 11) than extreme values (like 2 and 20), 2d10 is much more likely to give you a result closer to the average than a single die roll.
The same is true of 3d4 versus 1d10+2.
1d10+2 will give you an even distribution of outcomes (ie. equal chance of each possible total between 3 and 12). 3d4 will give you a much higher probability of an average total near 7 or 8, but much less chance of maximum or minimum damage.
