You're dividing an integer by an integer - that always uses integer arithmetic, even when you're assigning the result to a float
. The simplest way of fixing that is to make one of the operands a float, e.g.
float percent = (Score1 + Score2 + Score3) / 600f;
Note that this won't actually give you a percentage though - it'll give you a number between 0 and 1 (assuming the inputs are between 0 and 200).
To get an actual percentage, you need to multiply by 100 - which is equivalent to only dividing by 6:
float percent = (Score1 + Score2 + Score3) / 6f;