The mean and standard deviation of the average X bar are

A) mean = $1220 and SD = $270

B) mean = $1220 and SD = $22.82

C) mean = $122 and Sd = $270

D) mean = $122 and SD = $22.82

The probability that the average amount charged over these 140 procedures is less than $1200 is:

A) 0.5279

B) 0.8106

C) 0.1894

D) 0.4721

The critical value, z*, used for constructing a 99% confidence interval for a population mean mu is:

A) 1.645.

B) 2.054.

C) 2.326.

D) 2.576.