Let 'S' be the sample space of rolling dice once.
Assuming a dice is fair, all the outcomes are equally likely.
When a dice is rolled once, there are possible outcomes, when a dice is rolled twice, there are possible outcomes, and, when the dice is rolled times, there are possible outcomes.
Here, the dice is rolled times. Thus, the total number of possible outcomes are .
There are places available in each sequence, the number of ways of selecting exactly three
In the remaining places, the number of ways of selecting exactly three
In the remaining places, any number other than and can take place.
The number of possible ways of filling the remaining places
The total number of sequences with exactly three and three
Use the formula to compute the required probability: