A landline telephone number has 7 digits. How

Answered question

2022-03-30

A landline telephone number has 7 digits. How many different landline numbers are possible if it must not start with 0?

 

Answer & Explanation

user_27qwe

user_27qwe

Skilled2022-04-22Added 375 answers

If the numbers are repeatable, we have

9 numbers are able to fill in the first digit (1–9), 10 numbers for the other 6 digits (0–9).

 

Thus,

9×106=9000000 ways

 

If the numbers are not repeatable, we have

Numbers able to fill in the first digit : 1–9

For the second digit, there are 9 numbers, since one of the numbers has been used in the first digit.

For the third digit, there are 8 numbers and so on.

 

Thus,

9×9×8×7×6×5×4=544320 ways

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