If you roll two fair six-sided dice, what is the probability that the sum is 9 or higher?

The possible first numbers are 3 through 6 ... so for each first number you have a probability of:

(1/6) (1/6) = 1/36 (when first is 3)

(1/6) (2/6) = 1/3 (when first is 4)

(1/6) (1/2) = 1/12 (when first is 5)

(1/6) (4/6) = 1/9 (when first is 6)

So the probability of rolling 9 or higher is the sum of the above probabilities ...

1/36+1/3+1/12+1/9

(1+12+3+4) / 36

20/36

5/9 (≈55.56%)