Let X1, X2, and X3 represent the times necessary to perform three successive repair task...

Let X₁, X₂, and X₃ represent the times necessary to perform three successive repair tasks at a certain service facility. Suppose they are independent, normal rv’s with expected values μ₁, μ₂, and μ₃ and variances σ²₁, σ²_2,and σ²³, respectively.