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.

Answer 1

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 $10 \times 10 \times 10 \times 10 = \boxed{10,\!000}$.