Suppose Company 1's stock return ๐๐ is a random variable and takes three possiblevalues: {-0.1, 0.1, 0.2}. And Company 2's stock return ๐๐ is a random variable and takes twopossible values: {-0.3, 0.4}. The joint probability distribution ๐๐(๐๐, ๐๐) is given as follows:๐๐(โ0.1, โ0.3) = 0.1, ๐๐(0.1, โ0.3) = 0.2, ๐๐(0.2, โ0.3) = 0.2,๐๐(โ0.1,0.4) = 0.2, ๐๐(0.1,0.4) = 0.2, ๐๐(0.2,0.4) = 0.1.Please calculate the following:(a) Marginal distributions: ๐๐๐๐(๐ฅ๐ฅ) and ๐๐๐๐(๐ฆ๐ฆ). (4 points)(b) Mean: ๐ธ๐ธ(๐๐) and ๐ธ๐ธ(๐๐). (4 points)(c) Variance: ๐๐๐๐๐๐(๐๐) and ๐๐๐๐๐๐(๐๐). (4 points)
Question
Suppose Company 1's stock return ๐๐ is a random variable and takes three possiblevalues: {-0.1, 0.1, 0.2}. And Company 2's stock return ๐๐ is a random variable and takes twopossible values: {-0.3, 0.4}. The joint probability distribution ๐๐(๐๐, ๐๐) is given as follows:๐๐(โ0.1, โ0.3) = 0.1, ๐๐(0.1, โ0.3) = 0.2, ๐๐(0.2, โ0.3) = 0.2,๐๐(โ0.1,0.4) = 0.2, ๐๐(0.1,0.4) = 0.2, ๐๐(0.2,0.4) = 0.1.Please calculate the following:(a) Marginal distributions: ๐๐๐๐(๐ฅ๐ฅ) and ๐๐๐๐(๐ฆ๐ฆ). (4 points)(b) Mean: ๐ธ๐ธ(๐๐) and ๐ธ๐ธ(๐๐). (4 points)(c) Variance: ๐๐๐๐๐๐(๐๐) and ๐๐๐๐๐๐(๐๐). (4 points)
Solution
(a) Marginal distributions: ๐๐(๐ฅ) and ๐๐(๐ฆ).
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 ๐๐(๐ฅ):
๐๐(-0.1) = ๐(-0.1, -0.3) + ๐(-0.1, 0.4) = 0.1 + 0.2 = 0.3
๐๐(0.1) = ๐(0.1, -0.3) + ๐(0.1, 0.4) = 0.2 + 0.2 = 0.4
๐๐(0.2) = ๐(0.2, -0.3) + ๐(0.2, 0.4) = 0.2 + 0.1 = 0.3
For ๐๐(๐ฆ):
๐๐(-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
๐๐(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: ๐ธ(๐) and ๐ธ(๐).
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 ๐ธ(๐):
๐ธ(๐) = -0.10.3 + 0.10.4 + 0.2*0.3 = -0.03 + 0.04 + 0.06 = 0.07
For ๐ธ(๐):
๐ธ(๐) = -0.30.5 + 0.40.5 = -0.15 + 0.2 = 0.05
(c) Variance: ๐๐๐(๐) and ๐๐๐(๐).
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 ๐๐๐(๐):
๐๐๐(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 ๐๐๐(๐):
๐๐๐(๐) = ((-0.3 - 0.05)^2)*0.5 + ((0.4 - 0.05)^2)*0.5 = 0.06125 + 0.06125 = 0.1225
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