As of April 2006, roughly 50 million.com web domain names were registered (e.g., yahoo.com). (a) How many domain names consisting of just two letters in sequence can be formed? x domain names How many domain names of length two are there if digits as well as letters are permitted as characters? [Note: A character length of three or more is now mandated.] domain names (b) How many domain names are there consisting of three letters in sequence? [Note: All are currently taken.] X domain names How many of this length are there if either letters or digits are permitted? domain names (c) How many domain names are there consisting of four letters in sequence? x domain names How many of this length are there if either letters or digits are permitted? domain names (d) As of a certain date, 96,385 of the four-character sequences using either letters or digits had not yet been claimed. If a four-character name is randomly selected on that date, what is the pro that it is already owned? (Round your answer to four decimal places.)