A piece of dice is rolled four times.
The probability of getting one 5 in one throwing is
Let X be the number of times a 5 will be rolled.
Now, when a dice is thrown four times, the possibilities are
no 5
one 5
two 5
three 5
four 5
Then, the values of X are
X=0,1,2,3,4
In case of no 5 and one 5, there will be no repeataion.
Repeatation happens for X=2,3,4
So, the total number of trails of repeated event is 3.