How many 4-digit numbers (not starting with 0) are there which are not divisible by 5?

7200

Step-by-step explanation:

You can also do it in your head. In the numbers 1000 1009, the only ones divisible by 5 are 1000 and 1005. This pattern repeats for every group of 10. So for every group of 10 there are 8 numbers not divisible by 5.

How many groups of ten are there in the 4 digit numbers? the first one is 1000 and the last one is 9999, so there are just 900 groups of 10. 900 * 8 is 7200, which is the same answer.

Or did you want it done with a formula?