The mean amount for all of the invoices for your company last month is not known. Based on your past experience, you are willing to assume that the standard deviation of invoice amounts is about $260.

a. If you take a random sample of 100, what is the value of the standard deviation for x?
b. Using the 68-95-99.7 rule, the probability is about 0.997 that x is within what amount of the population mean µ?