Any number greater than 21.023 but smaller than 21.024 can be an answer, so there are an infinite number of answers.
Sure, 21.0231, 21.0232 or 21.0239 are good answers, but if you keep adding decimals, as long as the 21.023 stays the same, it's good. So a number like 21.0239789565 is also greater than 21.023 but smaller than 21.024 and therefore a valid answer. Even 21.023999999 fits your description.
I don't know if I made myself clear, but if you have any further question, go ahead and ask :)