answer all:

Some accounting firms give the client an option to pay a fee when the tax return is completed that guarantees tax advices and support from the accountant if the client were audited. A large accounting firm is trying to determine what fee to charge for nextyear's returns. In previousyears, the actual mean cost to the firm for attending a client audit session was $680. To determine if this cost haschanged, the firm randomly samples 35 client audit fees. The sample mean audit cost was $650 with a standard deviation of $75. Complete parts a and b below.

a) Develop a 90% confidence interval estimate for the mean audit cost.

The 90% confidence interval for the mean audit cost is $

,$

.

(Round to the nearest dollar asneeded.)

b) Based on your confidenceinterval, what do you think of the claim that the mean cost haschanged?

A.

The interval doesnotcontain the historical mean $680, which doesnotsupport the claim that the mean cost has changed.

B.

The interval doesnotcontain the historical mean $680, which supports the claim that the mean cost has changed.

C.

The interval contains the historical mean $680, which supports the claim that the mean cost has changed.

D.

The interval contains the historical mean $680, which doesnotsupport claim that the mean cost has changed.