Hi,
The probability of rolling exactly three 4's in 5 rolls of a fair die
P(rolling a four)= 1/6
P(not rolling a four) = 5/6
1/6*1/6*1/6*5/6*5/6
distinguishable orders of the five rolls/3fours and '2' others:5!/[3!*2!]=10
P(exactly 3 fours in five rolls) = 10*(1/6*1/6*1/6*5/6*5/6)