fiveteen
assuming you're just talking about fluid, there are 2 and 1/3 fifths in a half gallon. a fifth is 750 ml, where a half gallon in 1.75L or, 1750ml, in regard to spirits. This isn't a true half gallon though, it's actually about 5 fluid ounces short, but American metrics say close enough.
Yes.
five
3/5 is more than 1/2
A fifth is 1/5 of a gallon. Therefore, 2.5 fifths would be half a gallon.
there are eight half-pints in a half-gallon
7.5
There are 2.5 of them.
There are 2 quarts in half a gallon
1/2 US gallon is two quarts.
Fifths doesn't go into 2 and 1/2 evenly. It would be about twelve fifths.