Posted by **angela** on Thursday, May 13, 2010 at 8:11pm.

a 7 digit phone number has a 3 digit prefix followed by 4 digits.how many different phone numbers are possible??

- math -
**Damon**, Thursday, May 13, 2010 at 8:23pm
I assume 0 through 9 are allowed and repeats are possible. For example 000-0000 is allowed.

How many prefixes?

10*10*10 = 1,000

how many digits

10*10*10*10 = 10,000

so 10^3 * 10^4 = 10^7 = 10 million

I guess that is why they needed area codes.

- math -
**Kassen**, Friday, January 1, 2016 at 10:37am
7!=1*2*3*4*5*6*7=... (combinatoric)

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