Distribution A is normal with mean μ and standard deviation σ . Distribution B is normal with
mean 2μ and standard deviation equal to that of distribution A. The z-value for x = 180 from
distribution A is 1.0 and the z-value for x = 180 from distribution B is 0.5. Find μ and σ
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Verified answer
This is a system of equations problem:
1 = (180 - μ) / σ
0.5 = (180 - 2μ) / σ
Solve both for σ:
σ = 180 - μ
σ = (180 - 2μ) / 0.5
Simplify the second equation:
σ = 180 - μ
σ = 360 - 4μ
Since they are both equal to σ, they are both equal to each other:
180 - μ = 360 - 4μ
Add 4μ to both sides:
180 + 3μ = 360
Subtract 180 from both sides:
3μ = 180
Divide both sides by 3:
μ = 60. Now we know the mean. Let's find the standard deviation:
σ = 180 - μ = 180 - 60 = 120
Answer: μ = 60 & σ = 120