Question

5) Telephone numbers in the
United States begin with a
3 digit area code followed
by 7 digits. Area codes and
local telephone numbers
cannot begin with O or I.
How many telephone
numbers are possible?

Answer 1

Answer:

6,400,000,000 (6.4 billions)

Step-by-step explanation:

We have a total of 10 digits, and each digit was 10 possibilities of being filled, except the first digit of the area code and first digit of the telephone number, that have only 8 possibilities.

So if 8 digits have 10 possible values and 2 digit has 8 possible values, the number of possible telephone numbers is:

10^8 * 8^2 = 6,400,000,000 (6.4 billions)