Question

Suppose the CPA Practice Advisor reports that the mean preparation fee for 2017 federal income tax...

Suppose the CPA Practice Advisor reports that the mean preparation fee for 2017 federal income tax returns was $273. Use this price as the population mean and assume the population standard deviation of preparation fees is $100.

(a)What is the probability that the mean price for a sample of 20 federal income tax returns is within $16 of the population mean? (Round your answer to four decimal places.)

(b)What is the probability that the mean price for a sample of 60 federal income tax returns is within $16 of the population mean? (Round your answer to four decimal places.)

(c)What is the probability that the mean price for a sample of 121 federal income tax returns is within $16 of the population mean?(Round your answer to four decimal places.)

(d)Which, if any, of the sample sizes in parts (a), (b), and (c) would you recommend to ensure at least a 0.95 probability that the sample mean is within $16 of the population mean? (Select all that apply.)

20 customers

60 customers

121 customers

none of the above

Homework Answers

Answer #1

a)

for normal distribution z score =(X-μ)/σx
here mean=       μ= 273
std deviation   =σ= 100.000
sample size       =n= 20
std error=σ=σ/√n= 22.3607
probability = P(257<X<289) = P(-0.72<Z<0.72)= 0.7642-0.2358= 0.5284

b)

std error=σ=σ/√n= 12.9099
probability = P(257<X<289) = P(-1.24<Z<1.24)= 0.8925-0.1075= 0.7850

c)

std error=σ=σ/√n= 9.0909
probability = P(257<X<289) = P(-1.76<Z<1.76)= 0.9608-0.0392= 0.9216

d)

none of the above :as probability is less than 0.95 in each of above 3 cases

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