Given: The dices are thrown.
By using the formula,
P (E) = favourable outcomes / total possible outcomes
Total number of possible outcomes is 63 = 216
So, n (S) = 216
Let E be the event of getting total of 17 or 18
E = {(6, 6, 5) (6, 5, 6) (5, 6, 6) (6, 6, 6)}
n (E) = 4
P (E) = n (E) / n (S)
= 4 / 216
= 1/54
