An Associated Press article by Eileen Alt Powell discussed the changes that banks are making to the way they calculate the minimum payment due on credit card balances. The changes are being pushed by federal regulators. In the past, minimum payments were set at about 2% of the outstanding balance. Each credit card issuer is making its own changes. For example, Bank of America Corporation in Charlotte, North Carolina, went from a minimum of 2.2% of the balance to a flat amount of $10 plus all fees and interest due.

Suppose that a large California-based bank is in the process of considering what changes to make. It wishes to survey its customers to estimate the mean percent payment on their outstanding balance that customers would like to see. The bank wants to construct a 99% confidence interval estimate with a margin of error of 0.2 percent. A pilot sample of n  50 customers showed a sample standard deviation of 1.4%.

How many more customers does the bank need to survey in order to construct the interval estimate?