Question of the Day

The first step in solving the problem is to determine the likelihood of each slot’s occurrence. Say, then, that the likelihood of each of the 36 regular slots is x. Then the likelihood of each of the two special slots (0 and 00) is 3x. To solve for x, we note that the sum of the probabilities for all 38 slots is 1, so: 36x + 2(3x) =1 and x =1/42. This means that the probability for each special slot is 3/42 (or 1/14, but we won’t reduce the fraction here because we’re going to add it to another in a moment). The probability that (a) a red even number, will occur is 9*1/42, or 9/42. The probability that (b) a red 23, will occur is 1/42. The probability that (c) 00, will occur is 3/42. So the probability that (a) or (b) or (c) will occur is the sum of these probabilities, 9/42+1/42+3/42 =13/42. All of the other answers are designed to catch you if you make various simple mistakes. For example, answer choice C is designed to catch you if you decide that the denominator for each probability is going to be 38. The discussion above shows that this is not the case: there are 38 slots, but because they are differently weighted, none of them has a 1/38 chance of occurring.