What is the probability of getting a sum of 9 from two throws of a dice?

$\frac{1}{9}$

When a die is thrown the outcome can be any of the numbers from 1 to 6.

 If two dice are thrown the set  of outcomes that ensure the sum is 9 is {(3, 6), (6,3), (4, 5), (5, 4)}.

 The total number of possible outcomes is 6*6 = 36

This gives the required probability as 4/36 = 1/9