Mortgage lenders often use FICO ® scores to check the credit worthiness of consumers applying for real estate loans. In general, FICO scores range from 300 to 850 with higher scores representing a better credit pro. A lender in a mid-western town would like to estimate the mean credit score of its residents. What is the required number of sample FICO scores needed if the lender does not want the margin of error to exceed 20, with 95% confidence?