The fuel economy of a 2009 Lexus RX 350 2WD 6 cylinder 3.5 L automatic 5-speed using premium fuel is a normally distributed random variable with a mean of μ = 20.5 MPG and a standard deviation of σ =...

The fuel economy of a 2009 Lexus RX 350 2WD 6 cylinder 3.5 L automatic 5-speed using premium fuel is a normally distributed random variable with a mean of μ = 20.5 MPG and a standard deviation of σ = 1.25 MPG. (a) What is the standard error of X – , the mean from a random sample of 16 fill-ups by one driver? (b) Within what interval would you expect the sample mean to fall, with 90 percent probability? (Source: www.fueleconomy.gov.)