Given a single die
There are 6 numbers
The outcomes when observing an odd number = 1, 3, 5
the outcomes when multiple of 3 = 3, 6
the intersection between the outcomes are = 3
so, the number of outcomes = 3 + 2 - 1 = 4
so, the probability of tossing a single die and observing an odd number or a multiple of 3 =
