coefficient of variation

Joe

2009-11-23 2:35 am

10 ,18, 24, 30, 19, 22, 24, 20, 18, 25, 20, 22, 19

The coefficient of variation of this data would be ? %

In addition, in a local cellular phone area, company A accounts for 70% of the cellular phone market, while company B accounts for the remaining 30% of the market. Of the cellular calls made with company A, 2% of the calls will have some sort of interference, while 3% of the cellular calls with company B will have interference. Given that a randomly selected cellular call is one that has interference, what is the probability it came from company A ?

回答 (1)

用戶9112

2009-11-24 4:37 am

✔ 最佳答案

Coefficient of variation cv = σ/μ
μ = (10 + 18 + 24 + 30 + 19 + 22 + 24 + 20 + 18 + 25 + 20 + 22 + 19)/13 = 20.85
σ^2 = (10^2 + 18^2 + 24^2 + 30^2 + 19^2 + 22^2 + 24^2 + 20^2 + 18^2 + 25^2 + 20^2 + 22^2 + 19^2)/13 - μ^2
σ = 4.52
cv = 4.52/20.85 = 0.2169
Probability that a phone is from company A and has interference problem
= 70% * 2% = 0.014
Probability that a phone is from company B and has interference problem
= 30% * 3% = 0.009
Probability that a phone has interference problem
= 0.014 + 0.009
= 0.023
Given a phone has interference problem, the probability that it is from Company A
= 0.014 / 0.023
= 14/23

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