Need probability help on dice system

[Max_Killjoy]

Hopefully someone here is better at probability math than I am, or can point me to a good reference. Trying to figure out how to determine averages on rolled dice, but it's a different sort of setup.

The number of 10-sided dice is variable, but you can't keep more than 2 results, and the 2 are added together to get the final total. So if you have 3d10, you roll 3, keep the best 2, and add them together. Roll a 3, a 6, and a 7, and your final total is 13 (not 16).

What I need is the formula to figure out the odds of each total (2 to a 20) on any pool of X dice.



You might recognize this as the basis of the system in Yggdrasill, etc -- borrowed the core book, trying to figure out some of the mechanics. There are some places where I'm not sure the authors did their match homework -- for example, on a straight-up characteristic (Strength, etc) roll: the average character will not on average succeed against an average difficulty).

[CharonsHelper]

I'd recommend just using Anydice.

http://anydice.com/

[Max_Killjoy]

I don't see a way to tell it "roll Xd10, only add the highest 2 results".


EDIT: Found it.


EDIT2: it's claiming that there's a 0.00% chance to get a result of 2 on 5d10, keep the highest 2 and total. I know that's not true... even on 5d10, you could roll 5 ones.

[Max_Killjoy]

Before I forget again -- thank you for pointing that site out.

[Arctanaar]

EDIT2: it's claiming that there's a 0.00% chance to get a result of 2 on 5d10, keep the highest 2 and total. I know that's not true... even on 5d10, you could roll 5 ones.

Well, the probability of that happening is 0.00001 (or 0.001%, if you prefer), which means that the calculator is correct, assuming it rounds down to the nearest hundredth.

[BayardSPSR]

I'd recommend just using Anydice.

http://anydice.com/

Aha! I've been looking for something like this too. Wonderful.