# Math Question

• Apr 29th 2007, 09:25 PM
redraider717
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?
• Apr 29th 2007, 09:30 PM
ecMathGeek
Quote:

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.