The city fuel economy of a 2009 Toyota 4Runner 2WD 6 cylinder 4 L automatic 5-speed using regular gas is a normally distributed random variable with a range 28 MPG to 37 MPG.
(a) Estimate the standard deviation using Method 3 (the Empirical Rule for a normal distribution). (Round your answer to 4 decimal places.)
Standard deviation
(b) What sample size is needed to estimate the mean with 90 percent confidence and an error of ± 0.25 MPG? (Enter your answer as a whole number (no decimals). Use a z-value taken to 3 decimal places in your calculations.)
Sample size