28. Let X1, X2, and X3 represent the times necessary to perform three successive repair tasks at a service facility. Suppose they are independent, normal rv's with expected values l1, µ2, and µ3 and...

solve part d please

Extracted text: 28. Let X1, X2, and X3 represent the times necessary to perform three successive repair tasks at a service facility. Suppose they are independent, normal rv's with expected values l1, µ2, and µ3 and var- iances of, ož, and oz, respectively. а. If and of = o3 = Hi = µ2 = µ3 = 60 o = 15, calculate P(X1 + X2 + X3 < 200).="" what="" is="" p(150="">< x1="" +="" x2="" +="" x3="">< 200)?="" b.="" using="" the="" u;'s="" and="" o;'s="" given="" in="" part="" (a),="" calcu-="" late="" p(55="">< x)="" and="" p(58="">< x="">< 62).="" c.="" using="" the="" u;'s="" and="" o;'s="" given="" in="" part="" (a),="" calcu-="" late="" p(-10="">< x="" -.5x2="" —="" .5xз="">< 5).="" d.="" if="" m="" 3="" 40,="" 12="" —="" 50,="" из="" —="" 60,="" от="" —="" 10,="" o3="12," and="" o="14" x2="" +="" x3="">< 160)="" and="" p(x1="" +="" x2=""> 2X3). 여= 10, calculate P(X1 +