What is the probability of getting two numbers the same having three dices? I had this on my exam, it sounded super easy but isn't so.
Solution: I know that there are $$6^3$$ combinations for all three dices. Then I just wrote the following:
And the combinations that I want are: $$first-second:(1,1,x),(2,2,x),(3,3,x),(4,4,x),(5,5,x),(6,6,x)$$
$$second-third:(x,1,1),(x,2,2),(x,3,3),(x,4,4),(x,5,5),(x,6,6)$$ $$first-third:(1,x,1),(2,x,2),(3,x,3),(4,x,4),(5,x,5),(6,x,6)$$ wich gives me the combination of $6+6+6=18$ and final result $18/216$, which is incorrect. What am I doing wrong?