Question 7 - Variance and Standard Deviation of a Random Variable - Chapter 13 Class 12 Probability
Last updated at April 16, 2024 by Teachoo
Variance and Standard Deviation of a Random Variable
Variance and Standard Deviation of a Random Variable
Last updated at April 16, 2024 by Teachoo
Question 7 Find the variance of the number obtained on a throw of an unbiased die. Let X be number obtained on a throw So, value of X can be 1, 2, 3, 4, 5 or 6 Since die unbiased, Probability of getting of each number is equal P(X = 1) = P(X = 2) = P(X = 3) = P(X = 4) = P(X = 5) = P(X = 6) = 1/6 Hence, probability distribution The mean Expectation value is given by E(X) = โ2_(๐ = ๐)^๐โ๐๐๐๐ = 1 ร 1/6+2 ร 1/6+ 3 ร 1/6+ 3 ร 1/6+ 5 ร 1/6+ 6 ร 1/6 = 21/6 The variance of x is given by : Var (๐ฟ)=๐ฌ(๐ฟ^๐ )โ[๐ฌ(๐ฟ)]^๐ So, finding ๐ธ(๐^2 ) E(๐^2 )=โ2_(๐ = 1)^๐โใใ๐ฅ_๐ใ^2 ๐๐ใ = 12 ร 1/6+22 ร 1/6+ 32 ร 1/6+ 42 ร 1/6+ 52 ร 1/6+ 62 ร 1/6 = (1 + 4 + 9 + 16 + 25 + 36)/6 = 91/6 Now, Var (๐)=๐ธ(๐^2 )โ[๐ธ(๐)]^2 = 91/6โ[21/6]^2 = 91/6โ441/36 = (546 โ 441)/36 = 105/36 = 35/12 Hence, variance is ๐๐/๐๐