PROBLEM 9.(6 points) In order to estimate an average room-service delivery time

Question

PROBLEM 9.(6 points) In order to estimate an average room-service delivery time at a newly opened Hilton Hotel, 22 deliveries were randomly selected during one-week period. Their average delivery time was found to be 25 minutes with a standard deviation of 5.2 minutes. It is known that room-service delivery times are Normally distributed. Construct and interpret a 99% confidence interval for an average delivery time of all room-service delivery times in this hotel. (Round the boundaries to 2 decimal places). Answer:

Explanation / Answer

DF = 22 - 1 = 21

With 21 degrees of freedom and 99% Confidence interval the critical value is +/- 2.8314

The confidence interval is

Mean +/- t0.005, 21 * sd/sqrt( n )

= 25 +/- 2.8314 * 5.2/sqrt(22)

= 25 +/- 3.139

= 21.861, 28.139

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