Chapter 5 - Discrete Probability Distributions - 5-1 Probability Distributions - Exercises 5-1 - Page 263: 7

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Rule 1 — each probability must satisfy $0\leq P(X)\leq 1$ Here $P(12)=-0.8$ is negative, which is impossible for a probability. Rule 2 — probabilities must sum to 1 Let’s still check the sum: $0.3+0.5+0.7+(-0.8)=0.7$ That's also not equal to 1. This is not a valid probability distribution.