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P.m.f. given by a formula with a constant k: find the mean

This type of question, asked 2 times: 16 Apr 2026 S2, 12 May 2026 S2. All 2 questions below, oldest first.

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  1. Question 1

    16 Apr 2026 S2

    99
    If a random variable XX has a probability mass function P(x)={kx2,for x=1,2,3,40,otherwiseP(x) = \begin{cases} kx^2, & \text{for } x = 1, 2, 3, 4 \\ 0, & \text{otherwise} \end{cases}, then the mean of XX is ...

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  2. Question 2

    12 May 2026 S2

    99
    The probability mass function (p.m.f) of a random variable XX is p(x)=x+3k,x=−2,−1,0,1p(x) = \dfrac{x + 3}{k}, x = -2, -1, 0, 1 and p(x)=0p(x) = 0 otherwise, then the value of E(x)=…E(x) = \ldots

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