How do you solve this or what is the formula?

A telephone number consists of 7 digits, the first 3 representing the exchange. How many different telephone numbers are possible within 537 exchange?

Subhotosh Khan

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I suspect the student is looking for answers to take home test.

jiwonstr

7 digits. the first three are 537, so you don't care about them. the question asks you the number of combination you can put in last four digits. think about having four blanks ( ) ( ) ( ) ( ). there are no restriction to what number you can't put, thus you can use all 10 digits (including zero).

solution (10) (10) (10) (10) = 10 X 10 X 10 X 10 = 10^4 resulting 10,000 possibilities for last four digits.

Therefore your answer is 10,000 different telephone numbers are possible for your question.