How many 5- digit numbers are there in all the number system​

The smallest 5 digit counting number is 10,000

The largest 5 digit counting number is 99,999

The difference is 99,999 - 10,000 = 89,999

The trick is to remember that this means that, AFTER 10,000
there are 89,999 counting numbers to get to 99,999. This
discounts the beginning point so the actual amount of
5 digit counting numbers is 89,999 + 1 = 90,000