in an effort to protect themselves from debit card theft, some people keep a minimal amount of money in their checking accounts. a bank is interested in knowing how much money their customers keep in their checking accounts. they take a random sample of 128 of their customers’ checking accounts. the sample yields a mean of $766 and a standard deviation of $85. a plot of the sample data is roughly symmetric with no outliers. calculate a 99% confidence interval for the mean amount of money this bank's customers keep in their checking accounts.