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a) A bank has determined that the monthly balances of the saving accounts of its customers...

a) A bank has determined that the monthly balances of the saving accounts of its customers are normally distributed, with an average balance of $1200 and a standard deviation of $250.

i. What proportions of the customers have monthly balances between $950 and $1075?

ii. If a sample of 30 customers was randomly selected, what is the probability that the average of this sample will be between $950 and $1075?   

b) Suppose that you want to estimate the mean of the above customer’s population (Part “a” above) to within $50 with 95% confidence. What sample size should you use for this task?

Math   Statistics-And-Probability   
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