We get students to write the words in their standard form:
Thirty-five thousand, eight hundred twenty-five
which is: 35,825
Similarly Half-of-a-million which is 500,000.
We were not sure if we should have hyphens in between those words.
As ghotioutofh2o said, you shouldn't have "of". It is "Half a million" or "a half million", with no hyphens. I would be more likely to write "five hundred thousand". "Half a million" is really an interpretation of 500,000, not actually the representation of the number in front of you in words.
mmm another academician here states that using the words without 'of' (half a billion instead of half of a billion) makes it a slang. Is that so?
So now I have two questions:
1) should we use a hyphen
2) should we use the 'of'