Telephone numbers consist of ten digits; the first and fourth digits cannot be 0 or 1. How many telephone numbers are possible?

Answer 1

The decimal number system has 10 digits, 0-9.

Two digits may represent 100 values, 00-99. This is 10*10.= 100.

If the first digit may not be 0, this is 9*10.

If the first and fourth digits of a ten digit telephone number may not be 0 or 1, then the number of unique phone numbers is:

8*10*10*8*10*10*10*10*10*10