The fuel economy of a 2011 Lexus RX 350 2WD 6 cylinder 3.5 L automatic 5-speed u

Question

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 = 25.5 MPG and a standard deviation of = 2.25 MPG. (a) What is the standard error of 2formula74.mml , the mean from a random sample of 25 fill-ups by one driver? (Round your answer to 4 decimal places.) Standard error of 2formula74.mml (b) Within what interval would you expect the sample mean to fall, with 98 percent probability? (Round your answers to 4 decimal places.) The interval is from _____to____

Explanation / Answer

a)

Standard error (SE) = SD / SQRT(n) = 2.25 / SQRT(25) = 0.4500

b)

Z for 98% probability = 2.3263

Interval:

Mean - Z*SE to Mean + Z*SE

25.5 -  2.3263*0.45 to 25.5 + 2.3263*0.45

24.4531 to 26.5469

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