# As of April 2006, roughly 50 million .com web domain names

Chapter 3, Problem 29E

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QUESTION:

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? 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.]

b.  How many domain names are there consisting of three letters in sequence? How many of this length are there if either letters or digits are permitted? [Note: All are currently taken.]

c.  Answer the questions posed in (b) for four-character sequences.

d.  As of April 2006, 97,786 of the four-character sequences using either letters or digits had not yet been claimed. If a four-character name is randomly selected, what is the probability that it is already owned?

QUESTION:

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? 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.]

b.  How many domain names are there consisting of three letters in sequence? How many of this length are there if either letters or digits are permitted? [Note: All are currently taken.]

c.  Answer the questions posed in (b) for four-character sequences.

d.  As of April 2006, 97,786 of the four-character sequences using either letters or digits had not yet been claimed. If a four-character name is randomly selected, what is the probability that it is already owned?

Step 1 of 4

Given, As of April 2006, roughly 50 million .com web domain names were registered

a)

The claim is to find many domain names consisting of just two letters in sequence can be formed? And How many domain names of length two are there if digits as well as letters are permitted as characters.

There are 26 letters in alphabet. There are 26 possible ways to choose the first character and 26 possible ways to choose second

Therefore, the possible number of domains with two letters is n

n =

= 676

We have 10 digits and 26 alphabets

So, totally 36

There are 36 possible ways to choose  the first character as digits as well as letters and  36 possible ways to choose  the second character as digits as well as letters.

therefore , n =

= 1296