Nina tosses 2 number cubes labeled 1 to 6. what is the probability that the sum is equal to 5?

Probability = (nr. of ways it can succeed) / (total nr. of possible outcomes)

The first cube can come up in 6 different ways.  For each of those . . .
The second cube can come up in 6 different ways.
Total number of possible outcomes = 6 x 6 = 36 .

The toss succeeds if the sum is 5.
How many ways can that happen ?
1 . . . 4
2 . . . 3
3 . . . 2
4 . . . 1
Four different ways.

Probability = 4/36 = 1/9 = 11.1%