**Now, we can start to do some cool counting!**

**Let's figure out how many phone numbers there are in each area code:**

** Phone numbers have 7 digits...**

** What we'll do is pick the first digit, then the second digit, then the third, and so on. (Just like dialing!) This will allow us to use the counting principle!**

**OK, so the possible digits are:**

**Ten possibilities!**

**Pick the first digit:**

**Typically, I'd say that there would be 10 choices here... But, we can't start a phone number with a 0 or a 1... So, there are 8 possibilities here:**

**Now, we pick the second digit -- no restrictions here...**

**10 possibilities **

**and 10 for each digit after that:**

**Since we picked slot 1, then slot 2, and so on, we get to use the counting principle:**

**So, there are 8,000,000 possible phone numbers.**