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Old 08-23-2017, 11:36 PM   #7
Ulzgoroth
 
Join Date: Jul 2008
Default Re: Minor dice rolling/ probability question

Quote:
Originally Posted by RyanW View Post
Assuming my math is right:

The final roll of an "exploding" d6 is effectively a d5 (if it rolls a six, it isn't the last die) which will have an average value of 3.

The number of expected 6s rolled is the infinite sum of 5n/6^(n+1), which is 0.2. If each six adds 5 to the total, that's just 0.2*5 = 1.

The total average is just 3+1 = 4.

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If all 1s are rerolled, the number of expected 6s becomes the infinite sum of 4n/5^(n+1), or 0.25. The last die would average 3.5 (it's now effectively d4+1). So 0.25*5+3.5 = 4.75.

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I'm confused about your sums - shouldn't they be n*(1/6)^(n+1) and n*(1/5)^(n+1)? Cool way to do it though.
Quote:
Originally Posted by RyanW View Post
If only an initial 1 is rerolled, it gets just a little bit trickier, but brute force spreadsheet approximations still work just fine (you just have to have the first line use a different formula from the rest). I get 0.24 rerolls for a total average of 4.6.
Pretty easy to handle with my approach - especially when you've already determined that the value of a die roll with exploding 6s but no rerolled 1s is 4.

d = ((4) + 2 + 3 + 4 + 5 + (5+4))/6 = 27/6 = 4.5
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I don't know any 3e, so there is no chance that I am talking about 3e rules by accident.
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