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?

_____________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.]

________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?

________domain names

How many of this length are there if either letters or digits are permitted?

_______domain names

(d)

As of a certain date,93,695of 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 probability that it is already owned? (Round your answer to four decimal places.)