Question

is all the numbers 1-99 back to back divisible by 9

Answer 1

Technically, every number is divisible by any number. While it most times results in a decimal/fraction, that decimal/fraction is the answer.

Answer 2

If you want a whole number, then no not all of them are divisible by 9. If you can have either a whole number OR a decimal/fraction, then all numbers are divisible by 9.