Damus
gladstein · 41w
Just rolled double sixes 5 times in 8 rolls in backgammon… AI says the odds of that happening are: 1,175,463 to 1 We live in a world of black swans
Bert profile picture
I don’t agree:

This is a binomial probability problem. Each roll of a fair six-sided die is an independent trial with success probability \(p = \frac{1}{6}\) (rolling a 6) and failure probability \(1 - p = \frac{5}{6}\) (rolling anything else). We want the probability of exactly \(k = 5\) successes in \(n = 8\) trials.

The binomial probability formula is:
\[
P(X = k) = \binom{n}{k} p^k (1 - p)^{n - k}
\]

First, compute the binomial coefficient:
\[
\binom{8}{5} = \frac{8!}{5!(8-5)!} = \frac{8!}{5! \cdot 3!} = 56
\]

Substitute into the formula:
\[
P(X = 5) = 56 \left( \frac{1}{6} \right)^5 \left( \frac{5}{6} \right)^3 = 56 \cdot \frac{1^5 \cdot 5^3}{6^8} = 56 \cdot \frac{125}{1,679,616} = \frac{7,000}{1,679,616}
\]

Simplify the fraction by dividing numerator and denominator by their greatest common divisor (which is 8):
\[
\frac{7,000 \div 8}{1,679,616 \div 8} = \frac{875}{209,952}
\]

This fraction is in lowest terms. As a decimal approximation, this is about 0.00417 (or 0.417%).
3❤️1
gladstein · 41w
The math is beyond me, I will admit
volcanic · 41w
Pretty sure that formula is for rolling 6, 5 out of 8 times. nostr:npub1trr5r2nrpsk6xkjk5a7p6pfcryyt6yzsflwjmz6r7uj7lfkjxxtq78hdpu mentioned rollings 6s (two dices of 6), 5 out of 8 times.