## Wednesday, January 19, 2011

### So, When a Big Party Searches for Secret Doors...

In my CotMA Campaign, I have five regular players and ten (10) regular PC's... Whew!  When they search for secret doors that's A LOT of d6's to roll...

Well, it occurred to me that I could use probability to calculate the odds of finding a secret door when everyone is searching.  Then, I could just make one d% roll and tell them if they've found something.

One of my players is a math genius and he reminded me that when you calculate probability, it is often easier to calculate the probability of something NOT happening -- in other words, 5 in 6 times a given (human) character won't find a secret door...  If there's a whole bunch of folks searching; you multiply that 5/6 by 5/6 by 5/6...  You get the idea; then you subtract that % from 1 to get the odds of FINDING a secret door.  Easy peasy.  :)

Taking that into consideration, I whipped up the following Google Doc

http://tinyurl.com/secretdoors

You can head on over there and copy it to your account so you can use it.

Here's what it looks like for my group:

Cack and Vera are both elves, so there's a "2" in the "finding" column.  Oryx is a dwarf -- maybe he needs a "2" as well.  Sir Owyn has "an eye for irregularity" so although he's human, he gets a "2" as well.  Everyone else gets a "1".

When everyone searches, 92% of the time, they will find a secret door.  If a few humans don't search, you just knock a few of the rows off the bottom.  Of course, I can customize this at any time.

Hope you find that helpful!

cyclopeatron said...

Cool! (Although there is something kind of fun about rolling handfuls of d6s!)

Frank said...

Also, an interesting thing you can do with probabilities, if you have a single person searching for a secret door, with a 1 in 6 chance of finding the door each turn, you can make a table that shows the cumulative chance of finding the secret door (17% for one turn, 31% for two turns, etc.). Then you roll your d100. If it comes up 1-17, the door was found in one turn, 18-31, found in two turns, etc.

I have used this method to determine when the next random encounter happens.

If something causes an interruption before the event occurs, you drop the roll. If they try again later, you just roll a new d100. The rolls can be independent, just like if you roll the d6 once per turn. The d100 roll coming up 32-100 just reflects the probability the event didn't occur in 2 turns, no different than the d6 coming up 2-6 indicating the event didn't occur within 1 turn.

Frank

Jim said...

@Cyclopeatron -- agreed!

@Frank -- STOLEN! I'm building that chart RIGHT NOW! I use groups of circles (OOOOOO) to represent a turn. I can just roll d% and count over, make a little mark, and wait for time to elapse so the party can stumble into trouble! Brilliant!

Frank said...

And just in case it's not obvious, once you have a roll that determines that an encounter occurs on turn 5, once turn 5 is done, you just roll again to determine when the next encounter is, starting from turn 6. Of course you can pre-generate when encounters will occur for some specified time by rolling to determine when the 1st encounter occurs, then make a roll for the 2nd, etc. until the time is filled. The only time you can't roll in advance is when the results of an encounter change the probability of subsequent encounters (for example, if wounded characters result in a higher chance of encounter, or if a party can dig in to rest up and have a lower chance of encounters).

Frank

Dylan said...

Nice job. Thanks for making it a shared spreadsheet. This obviously helps whether a roll is necessary.

Joseph said...

Does that take into consideration the fact that all 10 characters can't search the same 10x10 section of wall at the same time?

Jim said...

@Joseph -- no, I guess it doesn't do that. :( I've handwaved that a bit, I guess. If the party is large enough and they are searching a room of reasonable size, 20x30 or so or a 20 to 30 foot section of corridor, I just roll once. Kind of a team effort to search the area, I suppose. YMMV.