Total events in throwing two dices simultaneously
n(S) = 62 = 36
Total events to get same digit at two dices and sum 9
A = {(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6), (3, 6), (4, 5), (5, 4), (6, 3)}
n(A) = 10
Probability to get same digit on dices or sum 9
= n(A)/n(S) = 10/36
= 5/18
Thus, required probability
= 1 - 5/18 = 13/18