For this problem, assume the balls in the box are numbered 1 through 9, and that an experiment consists of randomly selecting 3 balls one after another without replacement.

Question

What probability should be assigned to the event that at least one ball has an odd number?

Answer 1

odd numbers = 1, 3, 5, 7, 9
even numbers = 2, 4, 6, 8

you are looking for the probability of getting 1, 2, or 3 balls with odd numbers.

5/9*4/8*3/7 = probability of selecting one odd number

5/9*4/8*4/7 = probability of selecting two odd numbers

5/9*4/8*3/7 = probability of selecting three odd numbers

Either-or probability = sum of individual probabilities.