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  1. #1
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    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?
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  2. #2
    Senior Member ecMathGeek's Avatar
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    Quote Originally Posted by redraider717 View Post
    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.
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