The fuel economy of a 2011 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? (Round your answer to 4 decimal places.)
Standard error of X _____
(b) Within what interval would you expect the sample mean to fall, with 90 percent probability? (Round your answers to 4 decimal places.)
The interval is from ____ to _____