From a set of whole numbers less than 25, what is the probability of getting a number either divisible by 5 or divisible by 3?

The chance will be 6 / 13.

To answer this, let's list all the numbers that are divisible by 5 or 3.

0  3  5  6  9  10  12  15  18  20  21  24

There are 12 out of the 26 numbers, or 12 / 26 or 6 / 13.