# Normal Probability:Customer satisfaction at Bank of America

3. Quality Progress, February 2005, reports on improvements in customer satisfaction and loyalty made by Bank of America. A key measure of customer satisfaction is the response (on a scale from 1 to10) to the question: "Considering all the business you do with Bank of America, what is your overall satisfaction with Bank of America? Here, a response of 9 or 10 represents "customer delight." a Historically, the percentage of Bank of America customers expressing customer delight has been 48%. Suppose that we wish to use the results of a survey of 350 Bank of America customers to justify the claim that more than 48% of all current Bank of America customers would express customer delight. The survey finds that 189 of 350 randomly selected Bank of America customers express customer delight.

a. If, for the sake of argument, we assume that the proportion of customer delight is p = 0.48, calculate the probability of observing a sample proportion greater than the results of the survey. Do by hand.

b. Find the probability that the sample proportion obtained from the sample of 350 Bank of America customers would be within three percentage points of the population proportion.

Note- Use a 0.05 level of significance where needed.

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#### Solution Summary

The solution provides step by step method for the calculation of probability using the Z score. Formula for the calculation and Interpretations of the results are also included.