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 = 26.75 MPG and a standard deviation of = 3.5 MPG.

Within what interval would you expect the sample mean to fall, with 99 percent probability? (Round your answers to 4 decimal places.)

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 = 26.75 MPG and a standard deviation of = 3.5 MPG.

Explanation / Answer

Mean is 26.75 and s is 3.5

a) standard error is given as SE=s/sqrt(N)=3.5/sqrt(36)=0.583

b) 99% confidence interval gives z value of 2.576

thus lower bound is : mean-SE*z =26.75-0.583*2.576=25.2482

upper bound is : mean+SE*z =26.75+0.583*2.576=28.2518

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