The highway fuel economy of a 2016 Lexus RX 350 FWD 6-cylinder
3.5-L automatic 5-speed using premium fuel is a normally
distributed random variable with a mean of ? = 21.50 mpg
and a standard deviation of ? = 2.75 mpg.
(a) What is the standard error of X¯¯¯X¯ , the mean from a random
sample of 9 fill-ups by one driver? (Round your answer to 4 decimal
places.)
Standard error of X¯¯¯X¯
(b) Within what interval would you expect the sample mean to fall,
with 95 percent probability? (Round your answers to 4 decimal
places.)
The interval is from to