# Going crazy over probability problem

#### gaeborak

##### New Member
I'm working through the book Probability Demystified, which has been an okay refresher on basic probability, but is known to contain a lot of errors. Problem is, they don't publish errata. I'm wondering if someone would post a solution to this problem, because I think the one in the book is incorrect. The question is:

A phone extension consists of 3 digits. If all the digits have a probability of being selected, what is the probability that the extension consists of the digits 1, 2, and 3 in any order? Repetitions are allowed.

The book answer is 0.006, which looks like they did permutations of the digits 1-3 divided by 10^3. This doesn't seem to fit the problem to me. I think it would be (3/10)^3, which is 3^3 (the # of events where each slot has 1-3 with replacement) divided by 10^3 (the total # of events in the sample space). I'm probably overlooking something simple, but I don't trust this book anymore either. Thanks for any help.