On any one die, the probability of 1 is 1/6 and the probability of not 1 is 5/6
The three dice are independent so the probabilities combine in the binomial way:
P(n ones) = 3Cn Pn(1-P)3-n where P is 1/6 and the coefficient is the combination of 3 things n at a time.
I'll do one for you: P(one 1 ) = 3C1 (1/6)(5/6)2 the coefficient is 3
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