Theana wrote: ↑04 July 2025, 14:04
The question here is , just for the sake of argument, while yes theoretically 7 - or 5 or 10 or any other number - have the same chance to roll even if they have just been rolled, how often can happen to have the same number rolled 3 times in different games?
An interesting mathematical question!
It is easy to calculate that if you throw the Catan dice three times in a row, you have a 0.014275 = 1.4275% = 1:70 chance of getting 3 same results.
I.e., if you repeat it 70 times you expect (on average) to get one instance of three same results.
Thus, if your game is 72 moves long, you have 70 (overlapping) sequences of 3 rolls in this games and you should expect 1 such instance to happen.
But of course now it is getting a little bit more difficult mathematically. Because 1 instance on average means that some games have 0 instances and others have 2+ instances...
In 36.55% of all games (of length 72 rolls) you have 0 instances, i.e. there will be NO sequence of 3 repeating numbers.
In 37.05% of all games (of length 72 rolls) you have exactly 1 instance, i.e. there will be 1 sequence of 3 repeating numbers.
In 18.51% of all games (of length 72 rolls) you have exactly 2 instances, i.e. there will be 2 sequences of 3 repeating numbers. Note that a sequence 4-4-4-4 would be such a case because you have 4-4-4 twice in this sequence. But also the sequence 4-4-4-6-2-3-10-10-10 would be in this category.
In 6.08% of all games (of length 72 rolls) you have exactly 3 instances.
And so forth
Jontia already wrote that the probability of having at least one instance of 7-7-7 in one game is 23.5% (found by simulation).
Now I have added that the probability of having at least one instance of three same numbers in one game is 63.45% (found by calculation).
Summary: In approx. 2/3 of all games a threefold repetition should occur. But note that in half of these cases there are even multiple such threefold repetitions.
[edit: @Theana: Do these numbers feel right to you? Would you have guessed that there is a 1.43% chance of getting three same sums if you roll the Catan dice three times? Does it feel right that a 3-fold repetition should happen on average once a game? I would be very happy if your (very natural!) feeling was that it should occur less often. Because then it would explain why you felt the situation 7-7-7 as weird - and our discussion could lead to a satisfying result for both of us!]