Suppose we have three jars: A, B, and C. Jar A contains 2 red marbles and 1 blue marble. Jar B contains 1 red marble and 2 blue marbles. Jar C contains 2 red marbles and 2 blue marbles. We select a jar at random. The probability we select A is 1/4. The probability we select B is 1/4. The probability we select C is 1/2. From the selected jar, we choose 1 marble; all marbles in the jar have the same chance of being selected.