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Given the moment generating function m(t) = e3(e^t-1), find P(X=0), the first and second moments of X, and Var(X).

Mathematics

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Answers

3 parts
a

0.0498\text{0.0498}

b

3\text{3}

12\text{12}

c

3\text{3}

Step-by-step solution

5 steps

The given moment generating function (MGF) is m(t)=e3(et−1)m(t) = e^{3(e^t-1)}.
This is the MGF of a Poisson distribution with parameter λ\lambda. The standard MGF for a Poisson distribution is MX(t)=eλ(et−1)M_X(t) = e^{\lambda(e^t-1)}.
By comparing the given MGF with the standard form, we can identify that λ=3\lambda = 3.
Thus, XX follows a Poisson distribution with parameter λ=3\lambda = 3.
For a Poisson distribution X∼Pois(λ)X \sim \text{Pois}(\lambda):

  • The probability mass function is P(X=k)=λke−λk!P(X=k) = \frac{\lambda^k e^{-\lambda}}{k!}
  • The first moment (mean) is E[X]=λE[X] = \lambda
  • The second moment is E[X2]=λ+λ2E[X^2] = \lambda + \lambda^2
  • The variance is Var(X)=λVar(X) = \lambda

Part a· 2 steps

Find P(X=0)P(X=0)

  1. Use the Poisson probability mass function with λ=3\lambda = 3 and k=0k=0.

    P(X=0)=30e−30!P(X=0) = \frac{3^0 e^{-3}}{0!}
  2. Simplify the expression.

    P(X=0)=1⋅e−31=e−3≈0.049787P(X=0) = \frac{1 \cdot e^{-3}}{1} = e^{-3} \approx 0.049787

    The probability P(X=0)P(X=0) is 0.0498\boxed{\text{0.0498}}.

Part b

3\text{3}

Find the first and second moments of XX

  1. Calculate the first moment, E[X]E[X].

    For a Poisson distribution, E[X]=λE[X] = \lambda.

    E[X]=3E[X] = 3
  2. Calculate the second moment, E[X2]E[X^2].

    For a Poisson distribution, E[X2]=λ+λ2E[X^2] = \lambda + \lambda^2.

    E[X2]=3+32=3+9=12E[X^2] = 3 + 3^2 = 3 + 9 = 12

    The first moment is 3\boxed{\text{3}} and the second moment is 12\boxed{\text{12}}.

Part c

3\text{3}

Find Var(X)Var(X)

  1. Use the formula for variance, Var(X)=E[X2]−(E[X])2Var(X) = E[X^2] - (E[X])^2.

    Using the results from part (b):

    Var(X)=12−(3)2=12−9=3Var(X) = 12 - (3)^2 = 12 - 9 = 3

    Alternatively, for a Poisson distribution, Var(X)=λVar(X) = \lambda.

    Var(X)=3Var(X) = 3

    The variance Var(X)Var(X) is 3\boxed{\text{3}}.

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