   SEARCH HOME Math Central Quandaries & Queries  Question from Natalie, a student: How many 5 digits zip codes are possible if digits can be repeated? Hi Natalie,

If you can use any digit then you have 10 choices for the first digit, 0, 1, 2,..., or 9. Once you have chosen the first digit you have 10 choices for the second digit and hence 10 × 10 choices for the first 2 digits. Again, whichever of the 100 possible choices you have made for the first two digits you have 10 choices for the third digit and hence 10 × 10 × 10 choices for the first three digits.

Can you complete the problem now?

Some locations now have a 3 digit extension of the zip code, in effect giving an 8 digit zip code. How many of these are there?

I am in Canada and our postal code is 6 character long. They are a letter, a digit, a letter, a digit, a letter and a digit. My house is S4S 1T2. How many of these are possible?

Penny     Math Central is supported by the University of Regina and The Pacific Institute for the Mathematical Sciences.