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Explanation:
It's imperative to note the following: A random variable that follows the chi-square distribution has a mean of n and a variance of 2n, where n is the number of degrees of freedom. We could approach the question from two different perspectives:
i. Summation of independent variables
Since n = 2, , and
and are independent, which means:
, and
Therefore, for the total loss from the two projects,
Mean = 4 * $100,000 = $400,000 while Variance = 8 * $100,000 = $800,000
ii. Summation of two chi-square random variables
If A and B are two chi-square random variables with m and n degrees of freedom, respectively, then the sum of A and B is ALSO a chi-square variable with m + n degrees of freedom.
Therefore,
Working out the problem with this result gives the same values as above.
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Q.64 The random variable X denotes (in units of $100,000) the size of loss per project incurred in a particular investment company. In addition, assume that X follows a chi-square distribution with 2 degrees of freedom. A risk manager randomly chooses two such projects and further assumes that their corresponding losses are independent of each other. Calculate the mean and variance of the total loss from the two projects.
A
Mean = $400,000; variance = $200,000.
B
Mean = $200,000; variance = $400,000.
C
Mean = $800,000; variance = $400,000.
D
Mean = $400,000; variance = $800,000.