counting basics

Counting the  number of positive 5-digit numbers that  don't  contain an  odd digit = 

4 choices for the  1st digit  *   4 choices for each of the  other 5 digits  = 

4 * 5^4  =  2500

So the number of  positive 5-digit numbers containing at  least 1 odd  digit = (90,000 - 2500)  =

87500

EDIT TO CORRECT A MISTAKE !!!!

Cphill:

I think you made a typo in 5-digit numbers.

There are: 99,999  -  10,000  +  1 ==90,000 5-digit integers, and not 900,000.