A third to a half
What is the meaning that ? "A third to a half of the population are introverts." And how does the system work ? What is the systems name ?

Question

Answer

It means somewhere between one third (1/3 or 33.3%) and one half (1/2 or 50%) of people are introverts. I don't understand your other two questions.

Answer

Typically, the smaller number is mentioned first.  There are two or three answers to the question.  I will be there is three to five days.  The units are the same such as fractions, answers, or days.