The total number of different telephone numbers are possible in city is 6561.
A term permutation relates to a mathematical process that determines the number of possible arrangements of a given set.
Now, according to the question;
Because the first three digits are fixed, we must select the next four digits.
A total number of available telephone numbers is increased by selecting one of nine numbers for the fourth digit;
nine numbers for the fifth digit;
nine numbers for the sixth digit;
and nine numbers for the seventh digit.
Thus,
= 9×9×9×9
= 6561
Therefore, the total number of ways in which telephone numbers are possible in city are 6561.
To know more about the permutation, here
https://brainly.com/question/12468032
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