Question

suppose you roll one die. What is the probability of not rolling a multiple of 2?

Answer 1

1, 3 and 5 are not multiples of 2.
The probability of rolling a 1,3 or 5 is 3/6 or 1/2.
Another way to do the question:
Prob of NOT rolling a multiple of 2 equals 1 - prob of rolling a multiple of 2.
So prob of rolling a multiple of 2 (ie. 2, 4 or 6) is 3/6 or 1/2.
1 - 1/2 = 1/2.