Which expression correctly represents P[x], the probability of outcome x?

• A. The total number of outcomes divided by the number of ways x can occur
• B. The number of ways x can occur divided by the total number of possible outcomes
• C. The square of the number of ways x can occur
• D. The probability of all outcomes summed

Answer: (B)

Probability of a specific outcome is the number of ways that outcome can occur divided by the total number of possible outcomes, assuming all outcomes are equally likely. If x can occur in k different ways and there are N total outcomes, then P[x] = k/N. This means more favorable ways raise the probability, while a larger set of possible outcomes lowers it. The other forms don’t match how probability works: dividing total outcomes by favorable ways gives an inverted ratio, squaring the number of ways isn’t meaningful for a probability, and summing probabilities of all outcomes equals 1, not the chance of a single outcome.