IF we throw 2 dice then there are 6 possible outcomes of having same number on both dice, namely

(1,1),(2,2),(3,3),(4,4),(5,5),(6,6)

And total 36 possible outcome of throwing two dice.

Therefore probability of getting same numbers on both dice =6/36

Hence probability of not getting same numbers on both dice will be

1-probability( Getting same number on both dice)

=1-6/36

=30/36

=5/6