The first three digits of a university phone exchange are 452. If all the sequences of the remaining four digits are equally likely, what is the probability that a randomly selected university phone number contains seven distinct digits?

Question

The first three digits of a university phone exchange are 452. If all the sequences of the remaining four digits are equally likely, what is the probability that a randomly selected university phone number contains seven distinct digits?

anonymous · Answer

I have the answer to this, but my question really is, why is the sample space 10^4? where did the 10 come from?

anonymous · Answer

If anything, wouldn't the sample space be 7^4? Since there's 7 digits in a phone number, unless they are factoring in the area code, which would then make it become 10.

anonymous · Answer

Nevermind, I think I just answered my own question, haha.