SOLUTION: I am trying to help my son with this problem! Please show how you get the answer. Thanks! How many seven-digit phone numbers are available if a digit can only be used once and

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Question 1067865: I am trying to help my son with this problem! Please show how you get the answer. Thanks!
How many seven-digit phone numbers are available if a digit can only be used once and the first number cannot be 0 or 1?

Answer by solver91311(24713) About Me  (Show Source):
You can put this solution on YOUR website!


There are 8 ways to choose the first number (2 through 9). For each of these ways to choose the first number there are 9 ways to choose the second number (0 through 9 except the first number chosen). So there are 72 ways to choose the first two numbers. Then, for each of those 72 ways to choose the first two numbers, there are 8 ways to choose the third number (0 through 9 except the first two numbers chosen), and so on. In sum:



You can do your own arithmetic.

John

My calculator said it, I believe it, that settles it