According to a study, it takes ana verage of 330 minutes fortaxpayers to prepare

Question

According to a study, it takes ana verage of 330 minutes fortaxpayers to prepare/copy/mail return. An agency selects arandom sample of 40 taxpayers and find a S.D of the time to prepareis 80 minutes.

a) What assumption or assumptions do you need to make about theshape of the population?

b) What is the standard error of the mean in this example?

c) What is the likelihood the sample mean is greater than 320minuites

d) What is the likelihood the sample mean is between320min - 35min.

e) What is the likelihood the sample mean is greater than 350minutes

Explanation / Answer

(a) normal distribution (b) s = 80/sqrt(40) (c) z(320)= (320-330)/(80/sqrt(40) = -0.79057 P(z>-0.79057)= 0.7854 P(sample mean > 320) = 0.7854 (d) Find z(350); Find z(320)=-0.79057 Find P(z(350)-z(320)) = 0.7285 (e) Find P(z>z(350)) = 0.0569

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