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Suppose Company 1's stock return ๐‘‹๐‘‹ is a random variable and takes three possiblevalues: {-0.1, 0.1, 0.2}. And Company 2's stock return ๐‘Œ๐‘Œ is a random variable and takes twopossible values: {-0.3, 0.4}. The joint probability distribution ๐‘“๐‘“(๐‘‹๐‘‹, ๐‘Œ๐‘Œ) is given as follows:๐‘“๐‘“(โˆ’0.1, โˆ’0.3) = 0.1, ๐‘“๐‘“(0.1, โˆ’0.3) = 0.2, ๐‘“๐‘“(0.2, โˆ’0.3) = 0.2,๐‘“๐‘“(โˆ’0.1,0.4) = 0.2, ๐‘“๐‘“(0.1,0.4) = 0.2, ๐‘“๐‘“(0.2,0.4) = 0.1.Please calculate the following:(a) Marginal distributions: ๐‘“๐‘“๐‘‹๐‘‹(๐‘ฅ๐‘ฅ) and ๐‘“๐‘“๐‘Œ๐‘Œ(๐‘ฆ๐‘ฆ). (4 points)(b) Mean: ๐ธ๐ธ(๐‘‹๐‘‹) and ๐ธ๐ธ(๐‘Œ๐‘Œ). (4 points)(c) Variance: ๐‘‰๐‘‰๐‘Ž๐‘Ž๐‘Ÿ๐‘Ÿ(๐‘‹๐‘‹) and ๐‘‰๐‘‰๐‘Ž๐‘Ž๐‘Ÿ๐‘Ÿ(๐‘Œ๐‘Œ). (4 points)

Question

Suppose Company 1's stock return ๐‘‹๐‘‹ is a random variable and takes three possiblevalues: {-0.1, 0.1, 0.2}. And Company 2's stock return ๐‘Œ๐‘Œ is a random variable and takes twopossible values: {-0.3, 0.4}. The joint probability distribution ๐‘“๐‘“(๐‘‹๐‘‹, ๐‘Œ๐‘Œ) is given as follows:๐‘“๐‘“(โˆ’0.1, โˆ’0.3) = 0.1, ๐‘“๐‘“(0.1, โˆ’0.3) = 0.2, ๐‘“๐‘“(0.2, โˆ’0.3) = 0.2,๐‘“๐‘“(โˆ’0.1,0.4) = 0.2, ๐‘“๐‘“(0.1,0.4) = 0.2, ๐‘“๐‘“(0.2,0.4) = 0.1.Please calculate the following:(a) Marginal distributions: ๐‘“๐‘“๐‘‹๐‘‹(๐‘ฅ๐‘ฅ) and ๐‘“๐‘“๐‘Œ๐‘Œ(๐‘ฆ๐‘ฆ). (4 points)(b) Mean: ๐ธ๐ธ(๐‘‹๐‘‹) and ๐ธ๐ธ(๐‘Œ๐‘Œ). (4 points)(c) Variance: ๐‘‰๐‘‰๐‘Ž๐‘Ž๐‘Ÿ๐‘Ÿ(๐‘‹๐‘‹) and ๐‘‰๐‘‰๐‘Ž๐‘Ž๐‘Ÿ๐‘Ÿ(๐‘Œ๐‘Œ). (4 points)

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Solution

(a) Marginal distributions: ๐‘“๐‘‹(๐‘ฅ) and ๐‘“๐‘Œ(๐‘ฆ).

The marginal distribution of a variable is the probability distribution of that variable without considering the effects of the other variables. It is calculated by summing the joint probability distribution over all possible values of the other variable.

For ๐‘“๐‘‹(๐‘ฅ):

๐‘“๐‘‹(-0.1) = ๐‘“(-0.1, -0.3) + ๐‘“(-0.1, 0.4) = 0.1 + 0.2 = 0.3

๐‘“๐‘‹(0.1) = ๐‘“(0.1, -0.3) + ๐‘“(0.1, 0.4) = 0.2 + 0.2 = 0.4

๐‘“๐‘‹(0.2) = ๐‘“(0.2, -0.3) + ๐‘“(0.2, 0.4) = 0.2 + 0.1 = 0.3

For ๐‘“๐‘Œ(๐‘ฆ):

๐‘“๐‘Œ(-0.3) = ๐‘“(-0.1, -0.3) + ๐‘“(0.1, -0.3) + ๐‘“(0.2, -0.3) = 0.1 + 0.2 + 0.2 = 0.5

๐‘“๐‘Œ(0.4) = ๐‘“(-0.1, 0.4) + ๐‘“(0.1, 0.4) + ๐‘“(0.2, 0.4) = 0.2 + 0.2 + 0.1 = 0.5

(b) Mean: ๐ธ(๐‘‹) and ๐ธ(๐‘Œ).

The mean of a random variable is the expected value of that variable. It is calculated by summing the product of each possible value of the variable and its probability.

For ๐ธ(๐‘‹):

๐ธ(๐‘‹) = -0.10.3 + 0.10.4 + 0.2*0.3 = -0.03 + 0.04 + 0.06 = 0.07

For ๐ธ(๐‘Œ):

๐ธ(๐‘Œ) = -0.30.5 + 0.40.5 = -0.15 + 0.2 = 0.05

(c) Variance: ๐‘‰๐‘Ž๐‘Ÿ(๐‘‹) and ๐‘‰๐‘Ž๐‘Ÿ(๐‘Œ).

The variance of a random variable is a measure of how much the values of the variable vary around the mean. It is calculated by summing the product of the square of the difference between each possible value of the variable and the mean, and its probability.

For ๐‘‰๐‘Ž๐‘Ÿ(๐‘‹):

๐‘‰๐‘Ž๐‘Ÿ(๐‘‹) = ((-0.1 - 0.07)^2)*0.3 + ((0.1 - 0.07)^2)*0.4 + ((0.2 - 0.07)^2)*0.3 = 0.0027 + 0.00036 + 0.00513 = 0.00823

For ๐‘‰๐‘Ž๐‘Ÿ(๐‘Œ):

๐‘‰๐‘Ž๐‘Ÿ(๐‘Œ) = ((-0.3 - 0.05)^2)*0.5 + ((0.4 - 0.05)^2)*0.5 = 0.06125 + 0.06125 = 0.1225

This problem has been solved

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