Question

roll 2 standard dice and add the numbers. what is the probability of getting a number larger than 8 for the first time on the third roll?

Answer 1

Out of 36 possibilities for each roll, the total of greater than 8 can be obtained by:
6,3
3,6
4,5
5,4
5,5
5,6
6,5
6,6
So the probability of getting greater than 8 on a throw = 8/36
On the first two throws, each has a probability of getting 8 or less of (1-8/36).
If the events are independent, the probability of both/all events occurring is determined by multiplying the probabilities of the individual events.

I'll let you do the remainder of the calculations