# Normal Probabilities and t test for Mean

The amount of time a bank teller spends with each customer is normally distributed with a mean of 3.10 minutes and a standard

deviation of 0.40 minutes. (Use the z table)

If a random sample of 16 customers is selected from the bank, what is the probability that the average time spent per customer will be at least 3 minutes?

There is an 85 percent chance that the sample mean will be below how many minutes?

Doubting Thomas does not believe that the mean is actually 3.10 minutes since he has often waited longer. He decides to conduct a study and generates a random sample of 25 customers. He calculates the waiting time for all 25 customers and finds the average A waiting time to be 4 minutes. Based on this information, what is the best estimate of the population mean assuming 95 percent accuracy. Is the doubting Thomas correct in his assumption?

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#### Solution Summary

The solution provides step by step method for the calculation of Normal probabilities and t test for mean. Formula for the calculation and Interpretations of the results are also included. Interactive excel sheet is included. The user can edit the inputs and obtain the complete results for a new set of data.