Five automobiles of the same type are to be driven on a 300- mile trip. The first two will use an economy brand of gasoline, and the other three will use a name brand. Let X1, X2, X3, X4, and X5 be the observed fuel efficiencies (mpg) for the five cars. Suppose these variables are independent and normally distributed with m1 m2 20, m3 m4 m5 21, and s2 4 for the economy brand and 3.5 for the name brand. Define an rv Y by