1. ## Math Question

The U.S. Postal Service uses zip codes to route mail between postal offices. Zip codes are 5 digit codes made up from the digits 0-9 (10 digits in all).

If zip codes in Texas must begin with a 7 or 8 and digits can be repeated, how many zip codes are possible for the state of Texas?

2. Originally Posted by redraider717
The U.S. Postal Service uses zip codes to route mail between postal offices. Zip codes are 5 digit codes made up from the digits 0-9 (10 digits in all).

If zip codes in Texas must begin with a 7 or 8 and digits can be repeated, how many zip codes are possible for the state of Texas?
Here's how I know how to do this problem. There may be a more "technical" way to do it, but my way will work.

If we have 5 digit zip codes that MUST start with either 7 or 8, then 4 of the 5 digits can be any arangment of 0-9. That's 10 digits that can appear in 4 slots = 10^4 = 10000, and 2 digits that can appear in the first slot, which is 2*(10000) = 20,000.

However, if I'm mistaken, I would appreciate someone coming to correct me.