Telephone numbers usually have 9 digits. The first two digits represent the area code and remain constant. The last 7 digits represent the number and cannot begin with 0. How many different telephone numbers are possible with a given area code?

The total number of possible telephone numbers is determined by the number of possible combinations for the last 7 digits. Each of the 7 digits can be any number from 1 to 9 for the first digit (9 choices) and any number from 0 to 9 for the remaining six digits (10 choices each).
Thus, the total number of telephone numbers is:
9×106=9,000,000 possible telephone numbers.

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