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A probability mass function (PMF) for a DISCRETE random variable X has the property
AΣ p_X(x) over Val(X) equals 0
Bp_X(x) can exceed 1 for some x
Cp_X(x) is undefined at x = 0
DΣ p_X(x) over Val(X) equals 1
Answer & Solution
Correct answer: D. Σ p_X(x) over Val(X) equals 1
A PMF satisfies 0 ≤ p_X(x) ≤ 1 and Σ p_X(x) = 1 over all values X can take. PDFs (continuous case) can exceed 1 in value but their INTEGRAL is 1; this is a common confusion.
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