What is the next number after 1.9?

There is no answer to that question, as there are an infinite amount of possibilities without specifying something like the amount of decimal places. So if you were to say 1.9000000000000000000000000001, you could insert an infinite amount of zeros before the 1. Whereas were you to say what is the next number with 1 decimal place, then there is the answer 2.0 that can be given.