The local seven-digit telephone numbers In a city have 617 as the first three digits. How many different telephone numbers are possible in city A.
Since the first three digits are known to be 617, we only need to consider the last four digits.
Each digit can be any number from 0 to 9, so there are 10 choices for each of the four digits.
Therefore, the total number of different telephone numbers possible is $10 \times 10 \times 10 \times 10 = \boxed{10,\!000}$.