2. Problem: There are 680 three-digit numbers that are available for use as area codes in North America. As of April 2010, 301 of them were actually being used (Source: www.nanpa.com). (3 pts.)
a. How many additional three-digit codes are available for use?
b. Within a given area code, how many unique telephone numbers are theoretically possible?
c. As of April 2010, how many total phone numbers are possible in North America?

Question

2. Problem: There are 680 three-digit numbers that are available for use as area codes in North America. As of April 2010, 301 of them were actually being used (Source: www.nanpa.com). (3 pts.)
a. 	How many additional three-digit codes are available for use?
b. 	Within a given area code, how many unique telephone numbers are theoretically possible?
c. 	As of April 2010, how many total phone numbers are possible in North America?

anonymous · Answer

pattern is xxx xxx xxxx  10^10 possibles to start
given area code ccc xxx xxxx leaves 10^7 possibles

since there are  680 possible area codes multiple 680 x 10^7

anonymous · Answer

can you explain each step more clearly?

anonymous · Answer

It would take a bit of explaining.  I can tell you how he came up with 10^10 possibilities, then you'll understand the rest with ease.

A phone number has 10 digits in it, when represented by "x" a number is:
(XXX) XXX-XXXX

Each "X" can be 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, so there are 10 possibilities for each number in a phone number.  10 numbers each of which can be one of 10 numbers, 10^10.

anonymous · Answer

Does that make some more sense?