Question

find the rational numbers between 1/3 and 1/2,how many rational numbers can be determined between these two

Answer 1

There are infinitely many rational numbers in that slot. In fact, in ANY slot.

Here are a few of them

0.34, 0.35, 0.36, 0.37

0.40, 0.41, 0.4101, 04102, 0.41021, 0.41022, 0.410221, 0.4102210000001, etc.