A typical telephone number in the United States used to be digits. While you can still use a seven-digit code in most areas, a multitude of regions have begun using ten-digit telephone numbers. If the entire country goes to a ten-digit telephone, exactly how many different ten-digit telephone numbers will be available such that the first digit cannot be a or and the fourth digit cannot be a or a ?
Source: mathcontest.olemiss.edu 11/11/2013
There are choices for the first digit and choices for the fourth digit. For all other digits, there are choices .
different ten-digit telephone numbers.