Adie is rolled on a table. what is the probability of rolling a multiple of 3 or a number less than 5

The possible outcomes are {1, 2, 3, 4, 5, 6}.  How many of these outcomes are multiples of 3?  {3, 6}.  So the probability of rolling a mult. of 3 is 2/6, or 1/3.

How many possible outcomes might be numbers less than 5:  {1, 2, 3, 4 }.  Thus, the prob. of rolling a number less than 5 is 4/6, or 2/3.

What is the prob. of rolling a mult. of 3 OR a number less than 5?  These events are independent, so just take the 2 probabilities and add them together:  1/3 + 2/3 = 3/3 = 1.  This event has a probability of 1.0.