TheRPGSite
Pen & Paper Roleplaying Central => Pen and Paper Roleplaying Games (RPGs) Discussion => Topic started by: Bagpuss on February 28, 2006, 08:16:24 PM

Just what is the probability on a system where you roll X number of D10's keep Y number of them, and any natural 10's explode? It's making my head hurt just thinking about it.

Can someone at least work out the mean on an exploding D10.
IE: if it rolls a 10 you roll again and add.

open ended (high) D10 I'd say about 6.1 (which is roughly about 5.5 +5.5/10 )
if it's open ended (low) it changes a little bit, though ...
I'm not sure I understood the first question. You stated the system, but not the event you want to know the probability of :confused:
Not that I can actually answer it, my statistics are way too much rusted at this point :D
Chacal

Just what is the probability on a system where you roll X number of D10's keep Y number of them, and any natural 10's explode? It's making my head hurt just thinking about it.
I thought  but could easily be wrong  that any exploding die averages out to basically .5 over the mean.
So, an exploding d6 has a mean of 4. An exploding d8 has a mean of 5.
The fact that this matches Earthdawn's step numbers is no coincidence. :)
O

The fact that this matches Earthdawn's step numbers is no coincidence. :)
O
:eek: You said "Earthdawn" in a thread about statistics. I must wash my brain now !:D
Chacal

I wanted to know how to calculate the expected mean of whole load of dice combinations.
2k2
3k2
4k2
5k2
6k2
7k2
3k3
4k3
5k3
6k3
7k3
8k3
4k4
5k4
6k4
7k4
8k4
9k4
for example where you roll XkY dice X is the total number of exploding D10's you roll and Y is the number you keep the values off and add together to get the result.
So 1k1 is going to be 6.1, 2k2 is going to be 12.2, but how do you work out the values for the ones where you can discard the low rollers.

Interesting...
Lazy as I am, I tried google and wikipedia, but couldn't find an entry for these kind of questions. It's strange because they're asked for quite frequently on messageboards.
Chacal

Think I've found it...
http://www.umsl.edu/~ccb555/L5ROdds.xls
And this thread at AEG
http://www.alderac.com/forum/viewtopic.php?t=13206

Nice ! Thanks !
(you'd get rep if I could give it)
Chacal

I've been doing some playing around with the data for those links.
Assuming Attributes start at 2 and skills at 0. So obviously favouring clan/school attributes and school skills will make this slightly off.
It looks like the only way to get an average over 30 is to have Keep 4, or Keep 3 and a skill of 6+. Cheapest way is 4 in the attribute and 2 in the skill.
So if it wasn't for Mastery bonuses and Emphases it would always be best to raise attributes to 4 before raising skills much past 2. Although it's very hard to make fair comparisons with Mastery, Emphases and school/family bonuses.
I think we might have discovered a game its very hard to minmax.....
Well except for some of the stupid advantages.

Can someone at least work out the mean on an exploding D10.
IE: if it rolls a 10 you roll again and add.
Exploding die, I can do. I think. With A being the average result on the die:
A = (1+2+3+4+5+6+7+8+9+(10+A))/10 = (55+A)/10 = 5.5 + 0.1*A
0.9*A = 5.5
A = 5.5/0.9 = 6.11

This useful? Chance of hitting TN's going up in 5's, based on rolling 3k2 to 10k5 dice. I've removed any TN that was less than 10% chance to keep it to two pages.
What it clearly shows is 5k3 is better than 7k2. Buying a attribute from 2 to 3 is 12 CP's and buying a skill from 2 to 5 is also 12 CP's. So unless you have Emphases or gain a really good mastery from level 5 it's better to improve the attribute.

I don't play L5R and still find it useful :o
Chacal