The city fuel economy of a 2009 Toyota 4Runner 2WD 6 cylinder 4 L automatic 5-sp

Question

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 26 MPG to 33 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± 025 MPG? (Enter your answer as a whole number (no decimals). Use a z-value taken to 3 decimal places in your calculations.) Sample size

Explanation / Answer

a) here from empirical rule: as almost all values fall with in 3 std deviation away from mean

std deviation =range/6 =(33-26)/6 =1.1667

b)

(please revert )

for 90 % CI value of z= 1.6450 standard deviation = 1.1667 margin of error E = 0.25 required sample size n=(z/E)2                                         = 59

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