Registered: 10/25/01
Posts: 6974
Loc: Only 3rd world country in US
You do not join a percent sign to numerals with a hyphen under any circumstances. The % is actually part of the number--the number is 0.40 or 40%, forty hundredths whichever way you want to write it. Also, any time numerals are combined with symbols, you should avoid using the hyphen. In the first place, it is too easily mistaken for a minus sign; in the second, once you start multiplying modifying symbols, your numbers become very hard to read. For that reason, you do not use a hyphen to indicate a range between two percents. Write it out as 60% to 70% or whatever.
This is all covered in the BOS, but I don't feel like looking up the exact quotes at the moment.
BTW, the latest version of the BOS will tell you not to use hyphens with abbreviations for metric units of measure either.
Generally speaking, the less use you make of suspensive hyphens in any context, the better. (There are some medical publications whose style rules insist that they not be used under any circumstances. For transcription, at least try to minimize them.)
