something like this should work for you

DECLARE @Votes table ( VoteId int IDENTITY(1,1) NOT NULL,

Presenter char(3)NOT NULL,

VoteFor bit NOT NULL DEFAULT (0),

VoteAgainst bit NOT NULL DEFAULT (0) )

INSERT INTO @Votes VALUES ( 'JIM', 1, 0 )

INSERT INTO @Votes VALUES ( 'JIM', 0, 1 )

INSERT INTO @Votes VALUES ( 'BOB', 1, 0 )

DECLARE @TotalVotes int

SELECT @TotalVotes = SUM(CASE WHEN VoteFor = 1 THEN 1

WHEN VoteAgainst = 1 THEN -1

ELSE 0

END)

FROM @Votes

SELECT

V.Presenter,

V.Votes,

CAST(V.Votes * 1.00 / @TotalVotes as Decimal(3,2)) as VotePercentage

FROM (--get votes for presenter

SELECT

Presenter,

SUM( CASE WHEN VoteFor = 1 THEN 1

WHEN VoteAgainst = 1 THEN -1

ELSE 0

END) as Votes

FROM @Votes

GROUP BY

Presenter ) V