# How many 7-digit phone numbers can be formed in the first digit cannot be 0, and any digit can be repeated?

##### 1 Answer

This is an example of using an advanced counting scheme where we find the answer to be

#### Explanation:

We consider that each digit is selected independently of the others. This is a consequence of the statement that says digits can be repeated.

The first digit can be any of

Since each digit choice is independent, we just multiply all these choices together:

(Shows you why area codes have to come into play.)