Problem

A company buys a policy to insure its revenue in the event of major snowstorms that shut down business. The policy pays nothing for the first such snowstorm of the year and \( \$ 9300 \) for each one thereafter, until the end of the year. The number of major snowstorms per year that shut down business has a Poisson distribution with mean 1.9. Find the expected amount paid to the company under this policy during a one-year period.

Solution

Step 1 :Let X be the number of major snowstorms per year. X follows a Poisson distribution with \(\lambda = 1.9\). Then the expected number of snowstorms is equal to \(E[X] = 1.9\).

Step 2 :Define Y as the number of major snowstorms with payments, so \(Y = max(0, X - 1)\). Calculate the expected value of Y: \(E[Y] = \sum_{y=0}^{\infty} y \cdot P(Y = y) = \sum_{y=1}^{\infty} (y-1) \cdot P(X = y)\)

Step 3 :Calculate E[Y]: \(E[Y] = \sum_{y=2}^{\infty} (y - 1) \cdot \frac{e^{-1.9} \cdot 1.9^y}{y!} = e^{-1.9} \cdot \sum_{y=2}^{\infty} \frac{1.9^y}{(y-1)!}\)

Step 4 :Recognize that the remaining sum is the sum of a Poisson distribution with mean \(\lambda' = 1.9\) shifted by one unit: \(E[Y] = e^{-1.9} \cdot (\sum_{y=1}^{\infty} \frac{1.9^y}{y!} - \frac{1.9}{1!} - \frac{1}{0!}) = e^{-1.9} \cdot (e^{1.9} - 1.9 - 1)\)

Step 5 :Calculate the expected amount paid under the policy during a one-year period: \(E[Paid] = \$ 9300 \cdot E[Y] = \$ 9300 \cdot (e^{-1.9} \cdot (e^{1.9} - 1.9 - 1)) = \$ 12127.5764\)

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Source: https://solvelyapp.com/problems/8852/

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