Question

Zip code contains 4 digits. How many zip-codes can be created with digits 0−9 if you can use each digit only once and zip code can not start with 0.

Answer 1

9*10^3 = 9000

Answer 2

4 digits be pull out from numbers (0-9)

Just so you know (0-9)=(0,1,2,3,4,,5,6,7,8,9)=10digit

Digit 1 no zero we have (1-9) possibilities 9

Digit 2 zero can be included we have(0,1,2,3,4,5,6,7,8,) possibilities 9

Digit 3?
Digit 4?

Now would be
The complete possibilities would be??
9×9××??

Answer 3

oops. I allowed repetition. my bad.