Math Is Fun Forum

Luke Harusame

Guest

Permutations

Please help:

As of 2000, local seven-digit phone numbers could have the form XZZ-ZZZZ, where X is any digit 2 through 9 and Z is any digit 0 through 9.  (Of course, the Zs don't necessarily all represent the same digit.)  How many seven-digit numbers are possible under this plan?

I absolutely can't get this for the life of me.  The first thing I do is try and figure out how many possibilities each digit has.  Once that's done, I multiply the numbers, don't I?  So that would leave 8*10^6, making the answer 8000000.  But that makes no sense.  I remember there being another step, but I'm a day behind because I missed math class yesterday for a marching band event, so I seriously need some assistance. I'm pretty positive everything I did was wrong, so if you could point me in the right direction, I'd be more grateful than you could know.

krassi_holmz

Real Member

Registered: 2005-12-02

Posts: 1,905

Re: Permutations

yes! the answer is 8000000, but that's not permutations!~

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