SOLUTION: If the first three digits of someone's phone number (do not include area code) are 777, How many different phone numbers could they have? Please don't just give me and answer. I

Question 80736: If the first three digits of someone's phone number (do not include area code) are 777, How many different phone numbers could they have?
Please don't just give me and answer. I would like to know how to work this problem.
I know that there 7digits in a phone numer, and the first three digits are taken then there are 4digits availiable.
is it P=n/(n-r)! where n=7 and r=4 I am not sure.
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
If the first three digits of someone's phone number (do not include area code) are 777, How many different phone numbers could they have?
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The general counting rule is "if there are n ways to perform the 1st step
of a procedure and m ways to perform the 2nd step of the procedure, then
there are n*m ways to perform the procedure".
Your Problem:
Telephone Number 777-????
There are 10 ways to fill the 1st ?
10 ways to fill the 2nd ?
10 ways to fill the 3rd ?
10 ways to fill the 4th ?
--------
So, there are 1*1*1*10*10*10*10 ways to build the phone number.
There are 1*10^4 = 10,000 phone numbers that start with 777.
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Cheers,
Stan H.

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