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Hi guys I have a pretty simple question regarding the probability of rolling double 6 on 5 dice. I think rolling double 6 on 2 dice is 1/36 right, but I dont know how to find out on 5 dice. If one of you guys could explain I would be thankful.

Thanks!

For a single roll of a fair s-sided die, the probability of rolling each value is exactly 1/s; this is an example of a discrete uniform distribution. For n multiple rolls, with a s-sided die the possibility space is equal to sn. So, for n rolls of an s-sided die the probability of any result is 1/s^n.

I.e., 6-sided die to roll a number = 1/6. To get that number on two rolls is 1/6^2 or 1/6*1/6 or 1/36. So

1/6*1/6*1/6*1/6*1/6.

If you had to get a 5 or 6 (let's say to wound) that would be 1/3^n. But that also assumes you fail if you don't get them all, which in WHFB generally doesn't come up.

This just shows you the % chance a total success/failure. Each throw is still 1/6 or 1/3 or whatever and each throw has no memory of the throw that came before it (one of my favorite rules of statistics). If you throw 29 dice out of boredom and they are all 6's the last throw isn't 1/6^30% unlikely to occur. It's chance is simply 1 in 6. Because you didn't make the challenge beforehand to roll all sixes on 30 rolls. If you rolled all 3's or any combination of numbers it would be as equally unique as the one you did.

DukeRustfield wrote:I.e., 6-sided die to roll a number = 1/6. To get that number on two rolls is 1/6^2 or 1/6*1/6 or 1/36. So

1/6*1/6*1/6*1/6*1/6.

I think he's asking the odds of there being 2 6s among all 5 dice - as in 'what's the odds of rolling IF on a spell?'

It's a binomial distribution, and you can calculate these at sites like this one;
http://easycalculation.com/statistics/binomial-distribution.php

The answer is 16.1%.
On six dice its 20.1%
Four dice is 11.6%
Three dice is 6.9%
And of course 2 dice is 2.8%

sebster is right, although the probabilities he calculated are for getting exactly 2 6s. The IF chances are actually:

Two dice: ~2,78%
Three dice: ~7,41%
Four dice: ~13,19%
Five dice: ~19,62%
Six dice: ~26,32%

The answer is simple.

If you really need to roll it the probability is 0%
If you really don't need to roll it the probability is 100%
And if you don't mind either way the probability is whatever the maths say.

Airmaniac wrote:sebster is right, although the probabilities he calculated are for getting exactly 2 6s. The IF chances are actually:

Two dice: ~2,78%
Three dice: ~7,41%
Four dice: ~13,19%
Five dice: ~19,62%
Six dice: ~26,32%

Oh of course, silly me. Thanks for the correction.